Carburetor Assembly

Reply

  #1  
Old 01-06-15, 01:18 PM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
Carburetor Assembly

I'll be removing, completely disassembling and cleaning the carb off my '07 Honda CRF250X dirt bike and am looking for some advice on the proper way to reassemble it. Specifically, whether I should use a di-electric grease (e.g. CRC Technician Grade Dielectric grease) on the o-rings, throttle slide, jet threads, or any other parts. I'm pretty clueless when it comes to greases and lubricants as far as when and where to use which kind and where not to. Putting everything back together dry doesn't seem like a good idea.
 
Attached Images   
Sponsored Links
  #2  
Old 01-06-15, 02:45 PM
Temporarily Suspended
Join Date: Jul 2008
Location: NY
Posts: 10,986
I would ask the manufacturer, of the carb. Nothing is better than info from the horse's mouth. May I ask, what's the reason for the rebuild?
 
  #3  
Old 01-06-15, 03:11 PM
Forum Topic Moderator
Join Date: Mar 2005
Location: USA
Posts: 42,814
I've never used any grease when rebuilding a carb BUT I've never rebuilt one that new [complicated] either.
 
  #4  
Old 01-06-15, 03:25 PM
Temporarily Suspended
Join Date: Jul 2008
Location: NY
Posts: 10,986
Same here marksr, I never used grease either.
 
  #5  
Old 01-06-15, 03:46 PM
Banned. Rule And/Or Policy Violation
Join Date: Apr 2013
Location: USA
Posts: 4,297
There is no need for any form of grease in a carb.
Dielectric is for electrical connections.
 
  #6  
Old 01-06-15, 05:35 PM
Forum Topic Moderator
Join Date: Oct 2002
Location: Hamilton County, Ohio
Posts: 4,286
If you feel that you must do a total teardown, I would recommend taking pictures of each step and also notes on the procedure. This is not your old one barrel Rochester carb.
 
  #7  
Old 01-06-15, 06:56 PM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
Why am I doing it? Because I just bought the bike and it isn't idling without the choke, so I'll be tearing it down, cleaning the carb body and jets thoroughly, and replacing all the gaskets and o-rings (already bought the gasket kit). I'm also installing a different main jet and needle to richen things up (Hondas are notorious for coming lean from the factory). I won't use any grease then. I was searching around online and heard of others using a silicone grease on the slide and o-rings. Another site said to use a dab of petroleum jelly on the choke plunger for smooth operation. Is there no truth to these things?
 
  #8  
Old 01-06-15, 07:09 PM
Temporarily Suspended
Join Date: Jul 2008
Location: NY
Posts: 10,986
I could understand lubricating moving parts. That's about it.
 
  #9  
Old 01-06-15, 07:24 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 20,668
I've rebuilt plenty of carbs (not as a Pro) and never did anything more than maybe a shot of WD40 or silicone to get something to slide into place.

The mechanical parts are better off just being thoroughly cleaned. Thats why they put bushings and bearings where needed.
 
  #10  
Old 01-07-15, 11:57 AM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
I've rebuilt plenty of carbs (not as a Pro) and never did anything more than maybe a shot of WD40 or silicone to get something to slide into place.

The mechanical parts are better off just being thoroughly cleaned. Thats why they put bushings and bearings where needed.
And what about the rollers on the throttle valve? No lube on those either?
 
  #11  
Old 01-09-15, 09:43 PM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
I just got the carb off the bike and removed the float bowl and jets. Since the bike wouldn't idle without either the choke on or the throttle screw turned in substantially, I expected to see a clogged pilot jet. However, all the jets are clear. What else other than a clogged pilot would cause this? Maybe the float isn't set high enough? I haven't measured it yet, but will do so tomorrow. BTW, it's a 37 mm Keihin FCR carburetor.
 

Last edited by mossman; 01-09-15 at 10:23 PM.
  #12  
Old 01-12-15, 08:31 PM
Member
Join Date: Feb 2010
Location: U.S.A.
Posts: 248
I would run a compression check---could very well be leaking valves.
 
  #13  
Old 01-13-15, 07:03 AM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
I would run a compression check---could very well be leaking valves.
I'll definitely be doing a leak-down test.
 
  #14  
Old 01-13-15, 08:24 AM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
The service manual says to inspect the throttle valve plate for scratches or wear. Mine looks a little worn towards the bottom and the black finish wearing off. I scraped the plate with my finger and pieces were flaking off. Should I replace it?

Name:  20150113_080030_R.jpg
Views: 204
Size:  31.8 KB

Name:  20150113_080102_R.jpg
Views: 254
Size:  32.4 KB
 
  #15  
Old 01-14-15, 06:30 AM
Member
Join Date: Nov 2007
Location: MI
Posts: 2,413
It doesn't look bad but Mikuni and Keihin flat-slide carbs are pretty cheap online. If running a tag wire through the jets and spray cleaner through every orifice doesn't fix the idle IMHO I would replace it. Odds are good the wire & spray is all it needs.

I don't recall any of the 2-stroke carbs I've rebuilt as having a coating on the slide--but then my experience only goes up to 24mm. I think it's just carbon you're seeing.
 
  #16  
Old 01-14-15, 08:59 AM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
Well I went ahead and ordered a new valve plate just to be safe. Cost me $68, which seems outrageous, but that's the cost for piece-of-mind I suppose.
 
  #17  
Old 01-14-15, 07:54 PM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
I just picked at the valve plate again and it definitely looks like the finish peeling off, not carbon. Carbon wouldn't flake off in tiny squares. Good thing I'm replacing it.
 
  #18  
Old 01-17-15, 03:22 PM
Member
Thread Starter
Join Date: Mar 2009
Location: Northern Virginia
Posts: 3,315
Just finished a leak down test. Only 4% leakage!!! Valve clearances are all in spec, so the engine is in great condition. I'm a happy camper.
 
Reply


Thread Tools
Search this Thread
Display Modes
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 09:24 PM.