85 Honda Prelude Idle Prob

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  #1  
Old 04-11-03, 11:38 AM
JeepYJ
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85 Honda Prelude Idle Prob

1985 Honda Prelude
1.8L I4 (Dual Carb, Non FI)
5 speed tranny
89k mi.

When I start the car, it will idle and run correctly until it reaches operating temp. After it gets up to temp, it will not idle correctly and will backfire (exhaust only) during downshifting. I have replaced the plugs, wires, coil, and ignitor in the dist. I noticed when it would stall, a small puff of vapor would come out of the 2 rubber hose connections on the intake manifold that supply the vaccum to the motor. Could this leak in the manifold cause both the poor idle and backfire? I would really like to get some advice before I proceed. Thanks in advance.
 
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  #2  
Old 04-12-03, 09:35 AM
Joe_F
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That is usually timing related, although the carburetors on these early Preludes are complex and a nightmare when they do give trouble.
 
  #3  
Old 04-14-03, 06:16 AM
JeepYJ
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I too thought that it was a timing problem initially. I tried that approach first and it didn't fix the problem.
 
  #4  
Old 04-14-03, 09:36 AM
Joe_F
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How's the compression? When was the last time it saw any service? Carburetor rebuild?

As I said, these carburetors aren't worth a wooden nickel.
 
  #5  
Old 04-14-03, 11:57 AM
JeepYJ
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I actually took the car to a former honda mechanic. He did a full tune up about 3k miles ago. He told me about the problem with carbs not being worth a darn. about $3k for a new set from honda. I guess I was hoping to find the problem somewhere other than the carbs. Even rebuilds are about $500..

One other issue. When the motor starts running really rough, I can disconnect any one of the plug wires and it doesn't make a difference. It does get a good spark when held near the plug though??? Short of new carbs or a motor swap, I don't think there is anything else to try.

But with all 500 miles of vaccuum lines under the hood, it could be anywhere...

edit: Forgot to mention that the problem went away for a couple weeks
 
  #6  
Old 04-14-03, 12:54 PM
Joe_F
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What did the former Honda mechanic think the problem is?

If he did a tuneup, apparently, we can assume the problem is not there. I would say it's in the carburetors. Again, those carburetors give a lot of problems, and yes they can be rebuilt.

However, basic engine state should be taken. Is there good compression? Are there vacuum leaks? How's the timing? If the motor is on its way out, it makes zero sense to go any further until these are rectified or a decision is made as to the mechanical health of the vehicle.

If the guy is true Honda mechanic, he should have no problem doing the rebuilds for you. Might be a little better than 500 if he justs R&R's them for you. I believe you have to get these things synchronized as well.

It's a piss poor system and frankly, Honda should have dumped it in favor of EFI a lot sooner.
 
  #7  
Old 04-14-03, 01:08 PM
JeepYJ
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yes, they do have to be syncronized after they are rebuilt and need a propane enrichener to do it correctly (I believe for the idle).

I have done a fair amount of carb work on american motors and motorcycles but I may leave this one to the pros. If they are that difficult to mess with, It may be best just to let him do it.

I am going to fix a vaccuum leak (mentioned in the first post) I found on the intake manifold before I jump into the carb problem though.

Thanks for your advice... And I do agree, this carb system SUCKS!!! I wish I had the 2.0 instead.
 
  #8  
Old 04-14-03, 03:19 PM
Joe_F
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Sure. The carburetor cannot be adjusted if there are vacuum leaks, so that must be fixed first. It may even solve the problem.

2.0, 1.8, same thing. Money pits when they get old like this
 
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