B&S 4HP Quattro mdl 10A902 - engine fluctuating

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  #1  
Old 06-20-06, 07:20 PM
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Unhappy B&S 4HP Quattro mdl 10A902 - engine fluctuating

I have an issue with a B&S 4hp Quattro model 10A902 type 22733 E1 in which when started runs fine for about a couple minutes then the engine starts to fluctuate as in revs up then almost dies then revs then almost dies.

Never actually kept it running long enough to see if it would ever just quit on its own.

Replaced the spark plug and set it to correct gap, replaced the air filter element and the engine worked great for one use. However next attempt to use the mower/engine it started acting up again.

Any ideas as what to trouble shoot next? the points? the exhaust valve sticking? Possibly the muffler since it has never been replaced?

Not sure which way to go next on this. Thanks in advance for any assistance.
 
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  #2  
Old 06-20-06, 10:20 PM
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Shouldn't have points..... I'd go ahead and take the carb/tank off, separate them and clean the tank out and clean the carb out (through any and all holes as well, don't forget the fuel pickup tube at the end) and replace the diapragm and gasket (don't fold em, keep in mind how they go back on) and then make sure the windvane governor (little plastic flap, connected to the carb's butterfly, has a couple springs to the link) make sure its not sticky and moves freely. Make sure to clean up around here as well. Make sure thos springs aren't covered up with gunk. OR are missing and of course broken.
 
  #3  
Old 06-21-06, 01:08 AM
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I think if you'll replace the carburetor diaphragm, you'll solve the problem.
 
  #4  
Old 06-21-06, 05:44 AM
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There are two springs attached to the windvane governor however one of the springs does appear to be really weak... like it is just there as a back up...

I will attempt to pull the carb/tank off and proceed to clean them all and see what that brings... Will try to do so after work tonight, will post results once I get it all re-assembled.

If it safe to use a carb cleaner on the parts? like one of those used for automobiles...

If I need to get replacement parts is there a good source that you may know of? Is the information posted in one of the sticky's on the forum?

Thanks again for the replies! Gives me somewhere to start to try to fix this problem.
 
  #5  
Old 06-21-06, 12:37 PM
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If this motor has the carb setting on top of the gas tank I definitely agree with cheese, I have this happen on 2 different B/S motors, it is not necessary to remove the carb and don't mess with the springs if you can help it. The diapraghm sets between the tank and carb, drop the tank down, replace the diaphram and reassemble. Have a nice day. Geo
 
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Old 06-21-06, 04:41 PM
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woops, double post.
 
  #7  
Old 06-21-06, 04:42 PM
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Regular carb cleaner like for ex: gumout will do. Cleaning the carb and tank is just something I'd do, to prevent further problems. Do you have a local small engine shop around you? I can't remember if lowes or anything carries these types of parts.
 
  #8  
Old 06-21-06, 06:50 PM
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You're local NAPA store will have a book showing a lot of small engine stuff @ a good price. Try there
 
  #9  
Old 06-21-06, 07:23 PM
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the carburetor diaphragm, can that generally be picked up at a store or is it strickly an order type of part?

I cleaned everything tonight fired the engine up and it worked great for about 5 minutes then it started again. It is like the windvane governor is not getting enough wind from the motor and starts to fluctuate...

but I will definately search out the carburetor diaphragm and give that a try next...

Thanks again all.
 
  #10  
Old 06-21-06, 07:26 PM
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netspec1
Hopefully this may be of some help to you, I had a similar engine a couple of weeks ago with the same problem. After checking numerous things, coil, ignition gap(timing), fuel etc, I found out that those plastic carbs are notorious for warping. So if you happen to have a similar model kicking around that runs okay, maybe you can swap carbs just to see if that is the issue here. I did rebuild the carb on that model and it ran alot better but I still didn't eliminate the problem completely.

Hope this helps.

snoman
 
  #11  
Old 06-22-06, 10:36 PM
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This flucuation is called surging or hunting. It`s an indication that the engine is starving for gas.
The ignition coil or timing has nothing to do with it. It`s a fuel problem which can be caused by blocked orfices in the main jet, something blocking the pick-up tube going into the tank, air leaks, water in the fuel or even old fuel.

Check to see if the gasket for the plastic intake tube is loose or cracked ,(were the carb, connects and it runs underneath the ignition coil with 2 scews holding down) You need to Remove the blower housing, the air vane governor and the coil to get to it.
Also, is the primer leaking? Is there water in the gas?

No effense Snowman: But I`ve worked on these engines before the plastic carbs even came out. I`ve never come across a warped base on a plastic carb, only the zink carbs warped and there were kits to take care of it.
 

Last edited by mikesmalleng; 06-23-06 at 09:39 PM.
  #12  
Old 06-22-06, 10:57 PM
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These carburetors have no settings and the springs you see are for idle adjusment only.
If you seperate the carb from the tank, on the bottom of the carb you`ll find a post with a screen on it, remove the screen, take a small pocket screwdriver and pop the plastic jet out of the center post and clean it out good. (if you look close at the post you will see a flat spot on jet, pop it out from there and it should snap right back in.
 
  #13  
Old 06-24-06, 01:05 AM
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I've worked on a lot of these myself, and I will say from my experience that these carbs are notorious for warping. Sometimes they distort so badly that the main jet doesn't seal in place and gets loose.

I am sure the problem here can be solved with a new diaphragm. When you pull the carb off, you'll see a wrinkled spot in the diaphragm where the carb warped upwards between the 2 screw holes under the engine intake side of the carb and let the diaphragm pull out from under the carb. Generally, a new diaphragm and gasket will solve the problem. It will probably happen again in a few years, but it only takes a few minutes and a couple bucks to fix.
 

Last edited by cheese; 06-23-08 at 07:24 PM.
  #14  
Old 06-24-06, 04:35 AM
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okay okay now everyone...

I am going to try the diaphram next, have not had the time to locate someone locally but I plan on doing so today. I have taken the carb off and cleaned all the parts well and I still had the same result after about 5 minutes of running.

If I run into problems with the diaphram not working I will be back to get further ideas, if it works I will be back with Kudos for those that assisted.

Thanks
 
  #15  
Old 06-24-06, 07:18 PM
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Calm down now Cheese, I`m not disputing you or any of your comments. I`m just going by my experience, and your going by yours. There`s no question about the plastic carburetors warping, all thought I`ve never received any service bulletins on this problem, it can easily happen when someone tightens the screws down unevenly.
We can all learn from this site.
Mike
 
  #16  
Old 06-24-06, 11:17 PM
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i have a briggs and stratton quattro 10A902-1615E1 and something similar happened to me.

If you use fuel with ethanol in this engine, doesn't even have to be the full 10% ethanol mix, it will surge a lot and when mowing, and when you stop moving, it will try to die out, then come back up.

a quick drive to chevron regular 87 or supreme plus 94 fixed the problem. both regular and premium work great, just as long as there is no ethanol in it. regular fuel stopped my surging and it runs smooth as silk.

so what kind of fuel are you running?
 
  #17  
Old 06-25-06, 12:29 AM
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Don't worry Mike, i'm not excited. Just backing up snoman with a bit of my experience with these engines. You did say " I`ve never come across a warped base on a plastic carb"..but then said "There`s no question about the plastic carburetors warping".

I think I state my thoughts/opinions pretty "matter of factly", but I don't mean it to come across rudely. Once in a while I have to eat crow, and in those cases I do so willingly.
 

Last edited by cheese; 06-25-06 at 12:44 AM.
  #18  
Old 06-25-06, 01:38 AM
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Let me rephrase that, I have never came across a problem on these "Spint" carburetors where a warped base was the issue.
As you mentioned, in most cases a diaphragm kit would solve the problem if that was the problem, because their made of a softer more flexible plastic. Now on the older Briggs 900000 and 920000 (3 & 31/2 hp) vertical engines with plastic Vacu-Jet carburetors and automatic chokes, that`s a different story. They were made with a harder material and I found gas leaking between the base and tank on a regular basis. And they only had a diaphragm with no gasket. I`m sure you`ve noticed how much more stable or thick the surface on these Sprint and classic tanks are.

Come on,,,,,,give me a break I did`nt register here to compete with everyone. I have enough of that in my own shop.
I just enjoy helping other people with my 18 years of experience.
 
  #19  
Old 06-25-06, 10:04 AM
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Interesting on the ethanol in the gas.. never even knew that could be the cause.. Will need to use the remaining gas in a vehicle as I do believe this last time the gas can was filled it was with gas containing ethanol.

Also I hear that when you prime the engine with the primer bulb a stream of gas should be evident... I do not have that.. I still need to replace the diaphram... Just a matter of the time to do it... too many other things going, wish there was an engine failry to fix it. just kidding... need to rain to stop today so I can work..

Thanks again to all
 
  #20  
Old 06-25-06, 11:31 AM
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once you put in normal gas start the motor and after about 5 min and you should start noticing a little difference. it should stop surging completely after one full tank's been used (dunno why this is, probably cause there is some fuel left over in the motor) i usually get full peformance back after the first tank has been used with normal gas.

if it still persists then you should replace the diaphragm, my quattro was made in made in March 1999 (code: 99033154) and was recently put to commercial use about 3 years ago. (runs about 3 hrs every 1 - 2 days) i've never had to replace the diaphragm, and I did leave old gas in it last year during the winter and it started right up. but try it out and see what happens.

and one last thing. with this ethanol gas i had, it would always run perfect the last minute before it runs out of gas. fill it back up again and it would surge.
 
  #21  
Old 06-25-06, 02:36 PM
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yeah the last time the tank was run down to empty the last minute of that tank it ran like a charm... hmm really wondering now if the gas is the issue... something about ethanol... Why cant we run mowers off of the grass clippings they create.. things that dont make you go hmmm
 
  #22  
Old 06-25-06, 03:25 PM
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yep just run it one or two tanks of regular gas and it should be fixed, same symptoms i had.

by the way, ethanol is made from wheat, similar to grass clippings
 
  #23  
Old 06-26-06, 01:18 AM
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Ethanol gas is not reccomended in small engines. I was unaware that you had it in there, and it could be the cause of your problem. We don't have ethanol gas near my area, so it's something I don't even consider when looking for a problem on a mower. I have no idea what effects it might have, but James might be on the right track. I'd be interested to hear the results.

Mike, I'm not trying to compete nor do I wish to. Lets let it drop, ok? I have no qualm at all with you, and never did. My job is to answer these posts with the information I have obtained through my years of experience...and that would be that these carbs do warp. Maybe that hasn't been proven to you in your experience yet. No problem. You can't be thin-skinned on a forum like this, because words and text don't convey emotion correctly all the time. Keep in mind that just because someone disagrees, it doesn't mean they are attacking you. If you still have any issue you'd like to resolve, please do so in a private message or email instead of this person's thread. This isn't the place. Thanks.
 

Last edited by cheese; 06-26-06 at 01:35 AM.
  #24  
Old 06-26-06, 06:42 PM
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Out here the cheapest low grade gas sold is what`s called, "gasohol". It`s a combination of gas and alcohol. I encourage customers not to use this because it can interfere with the proper air/
fuel mixture. But worse it leans out the engine causing the valves to burn and leak which will result in overheating from loss off compression and cause engine failure. It will also cause gasket shrinkage.This can turn out to be an expensive repair.
It may be nation wide. Its found at ARCO and THRIFY gas stations.
 

Last edited by mikesmalleng; 07-08-06 at 07:37 PM.
  #25  
Old 07-08-06, 06:46 PM
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Help

I am from Massachusetts and we now have gasohol. When they made the switch, my Dodge Caravan started running crappy and my 1974 Simplicity lawn tractor runs for a few minutes, then quits and won't start again. I've spentweeks trying to fix this and I've replaced everything replacible and flattened the head and the problem remains! This forum provided the answer!

Kind off pisses me off that the numbsculls at epa did this without seeing the consequenses. I don't want my car OR tractor motor to burn out!

Question; is there an additive or source for normal gasoline around here?
 
  #26  
Old 07-08-06, 07:43 PM
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Small engines need lead that was in "regular gas" some of the 89 octane unleaded fuel have a led substitute. Check with some of the auto parts stores, they may have a lead additive.
 
  #27  
Old 07-09-06, 01:00 AM
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??? No need to use lead substitutes. You can read it in your owner's manual...for the past couple of decades, small engines manufacturers have been reccomending unleaded fuel.

I have paid a bit of attention to fuel reccomendations in manuals since this thread came along, and most of them do make note that there may be performance issues related to ethanol fuel in fuels with higher percentages of ethanol, and some warned not to use methanol fuel at all, but ethanol was ok. Since we don't have it in my area, I haven't been able to see the effects for myself, but after reading this post, I think I will remember not to use it if it does appear at the pumps near me.
 
  #28  
Old 07-09-06, 09:51 AM
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in my manual it says no more than 10% ethanol and at my pumps, there are to, 90 octane with up to 10% (the cheap stuff) and 94 with at least 10%. They both never ran good in small engines. In my 11HP tractor, it runs ok, but sputters every down then.

I just use regular premium 94 octance gas without ethanol. runs the best in all my engines, beter than 87 or 89.
 
  #29  
Old 07-09-06, 10:47 AM
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The proportion of ethanol has been set at 10% for some time. When it first came out a number of years ago the discussion was pretty much what you see here, about the negative effects it would have. Most of it centered around destruction of nylon parts in fuel systems, primarily automotive applications. Eventually auto manufacturers backed off the dialogue to stay away from it and voiding warranties if used.

It is the same thing you find in a lot of gas line antifreeze. It adds a couple of points to the octane rating of the unleaded it has been added to, consequently it is considered to be a combustion modulator.

Being from Iowa we have had it here since it started. We use it in just about everything without any noticeable difference. It is cheaper at the pumps, I believe because of a subsidizing of the road use tax by the government to promote the fuel. Much of its support comes from being a renewable resource and less U.S. dependance on foreign oil.

I've never seen any damage that could be conclusively attributed to its use, but we all have different experiences with everything. I do believe it is here to stay with more ethanol plants going up all the time and the development of biodiesel.

To quote one of my neighbors "We gotta do sumpthin' with what the pigs don't eat."

Later
 
  #30  
Old 07-11-06, 06:42 AM
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Same Motor, same Problem

Folks,
My Weedeater (B&S 4.0 Quattro) has exactly the same problem as described in the other posts. Cleaned the carb, replaced the diaphram and it still surges. So now I'm looking at the gas issue.
The only problem is this, the only gas within 100 miles is 10% ethanol treated.

Would kicking the octane rating up prove effective? If so, any ideas as to what would work?

Great help and I really appreciate it.
Thanks
Charliefox
 
  #31  
Old 07-11-06, 09:24 PM
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In these cases, I would say that if the engine ran fine with the ethanol gas before, then it should continue to run fine with ethanol gas. If the problem started immediately after filling up with the first tank of ethanol blend you've ever put in it, then the fuel may well be the problem.

If it ran fine on ethanol blend before, and now it doesn't, I still think the diaphragm is the most likely culprit.
 
  #32  
Old 07-11-06, 10:25 PM
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try cleaning out the combustion chamber deposits. my cylinder head had about 2 mm of carbon on it, same for the piston. it ran better, but not perfect. must be related to the ethanol. can that dirty up the engine?
 
  #33  
Old 07-11-06, 10:36 PM
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Check your intake tube gasket or if the screws are loose or if it`s cracked. The plastic tube the carburetor connects to and runs under the ignition coil. Any air leaks in this will cause the engine to surge (fluctuate).

It may be hard to tell if it`s loose while the end of it is in the control bracket. you may have to remove the bracket to actually find out if this is the problem. I run in to it all of the time on "Classics, Quantum's, and Inteks. Some times I just take it off and either replace the gasket or put silicone on the old one as a process of elimination
 
  #34  
Old 07-12-06, 06:28 PM
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Two of the quotes from above say the engines ran very well as the fuel tanks ran empty. This is when the fuel/air mixture would be leaning. If you had to run the gasohol fuel I would look at this as a solution. Possibly rejetting the carb internally and making external adjustments would take care of it.

Adding ethanol to gasoline adds a couple new properties. One is it drops the combustion temperature which reduces some of the air pollutants. This is one reason it interests California. The other is it absorbs moisture which is carried into the combustion chamber to be burned with the fuel. This is why it's used in gasline antifreeze solutions. It should always be stored in sealed containers and not left in engines stored for long periods of time.

Gasohol that has been exposed to high humidity conditions could take take on enough moisture to affect its performance. In automotive applications with fuel injuection, the oxygen sensor would be telling the computer of the auto/truck to adjust the mixture and you would likely never notice the difference. A small engine doesn't have that advantage.

Hope this helps
 
  #35  
Old 07-15-06, 06:26 PM
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Talking solution

I did a search on "octane reducers". One English site said that there were several possibilities. The best, with the least problems is "Heptane". Yeh, just try to find that! Minimum order is 55 gallons.

Next was Kerosene. One pint per gallon of gasohol. One possible drawback is that it may disolve the cylinder glaze. I called a north east petroleum wholesaler to see what he thought. He said it probably wouldn't hurt the motor, as K has more lubrocity than gas. So I tried the Kerosene and for good measure I got one of those hot spark plugs, that Home Depot is selling, with the funny tip. The motor kicked off in less than 2 seconds and I mowed the field with no problems, no sputtering. Worked great!

Just a little more info, he said I could also use diesel fuel at the rate of 1/2 pint per gallon with the same result.

The big surprise for me was that it didn;t smoke one bit!

Thanks for the help. I'll be back!
 
  #36  
Old 07-29-06, 12:28 PM
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I have not been able to run two full tanks of premium gas since I decided to give that a try. I can say it is running better, however not at full speed... Went and held the throttle open with a finger to bring it to full speed and it ran incredibly better. Now that plastic flapper that regulates the speed, is that used for something special or can that be bypassed? At least until I can get two full tanks of premium run through... As far as ethanol in my area, had a 5 gallon gas can and the gas was bought prior to all the stations switching to the 10% blend...

Once I get the second full tank run through I am going to see if there is still the fluctuation. For now I have the throttle held at full speed with a wire to prevent that plastic flapper from causing the engine to surge...

This forum has been a big help hopefully I will have this issue solved soon and can call this a closed issue...
 
  #37  
Old 07-29-06, 12:54 PM
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If you are using gas that was in a 5 gal can purchased prior to when you stations switched, it's a wonder your motor runs at all, even if it had stablizer. Any gas stored longer than 90 days should not be used in small engines, dump it in your auto or something. Small engines can take a lot of abuse but old gas is not one of them. I would suggest you dump a quality fuel system cleaner in the poor thing if you can keep it running, while you are burning those 2 tanks of gas. Oh, and have a nice day. Geo
 
  #38  
Old 07-29-06, 08:10 PM
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Okay the english language plays havoc again... I did say it was a 5 gallon gas cann but the gas was not older than a year and half tops... plus in my town the gas stations just recently went to the 10% ethanol mix just over a year ago through out the entire city... Now it is difficult to find non ethanol anywhere... The bigger cities went to the ethanol blend a long time ago in the major big name stations, but in this little town it was not a big concern... heck we dont even have emisions testing here for cars... yet that is...

The mower ran extremely well with the gas from prior to filling it recently, so the older gas was a charm and wish I had more of that gas...
 
  #39  
Old 06-23-08, 02:33 PM
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10a902

Okay my B&S mower, 10a902, is surging and blowing out white smoke. When it surges it shakes the mower, like it is back firing. I've replaced the Carb, spark plug, blade. I took the carb off before replacing it cleaned it with carb cleaner. I took the gas tank off, drained it. Then refilled it. I've checked the crankshaft it isn't bent. The spark plug was the recommended spark plug for my mower from lowes. I've also ran liquid carb cleaner through the gas tank and mower. PLEASE HELP
 
  #40  
Old 06-23-08, 03:07 PM
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You should start a new Thread, the one you attached to is 2 yrs old, anyway, the white smoke is oil so check the oil level to see it isn't overfull, did you hit something it sorta sounds like you may have a partially sheared flywheel key, also during all this cleaning did you replace the diaphram if not see instructions below.
You need to install a new diaphram kit, it is Briggs part # 795083 or old # 495770 also Lowe's has a kit #5083 which has the same parts.

Here we go;
Remove air cleaner, there are 2 bolts that hold things together, one on the front of the tank 3/8" and one into the block 1/2", remove these bolts, now "slowly" slide the carb/tank off the intake tube and breather tube, now tilt the tank in to release the throttle linkage and waalaa the carb/tank is removed. Remove the 5 screws from the carb/tank remove carb(don't loose the spring) now spray all holes, cracks and crevases in both the carb and tank surface with brake parts cleaner, remove the main screen(looks like a thimble) with a small screwdriver pry out the main jet(carefully) and clean it, reinstall the jet, it can be difficult some times to get it to snap back in place(I use the rounded end of a screwdriver handle). Remove and clean the fuel pickup stem. Clean any junk/rust from the tank. Install the diaphram on the tank then the gasket(no goo or sealer) now carefully replace the carb(the spring will try to misalign the diaphram), tighten all screws a little at a time so as not to crimp the diaphram until they are all tight. Install the carb/tank in reverse order and you are done. If I missed something one of the real mechanics will correct me. Have a good one. Geo
 
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