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Won't idle or start after rebuild

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Please help. I'm getting very frustrated.

I just received my engine back after getting new piston, rings, kibblewhite valves, springs, head work.

After putting the engine back in I couldn't get it to fire by kicking over. Hooked it to a vehicle and towed it and it will fire when I give it some throttle. Figuired it must be a pilot jet issue so went through the carb and cleaned everything well. Same problem.

I've been through the carb 3 times now, checked valve clearances, cam timing and just about anything else I can think of.

I cannont get the bike to fire by kicking it over, but as soon as I hook up to a tow and crack the throttle it fires right away. I cannot get it to fire by kicking even with cracking the throttle.

The bike will also not idle. To keep it idleing I have to turn the idle up pretty high. When I start backing off the idle speed it goes from high idle to dead.

Any ideas would be appreciated.

The engine also runs hot, but I figuired that may be because i'm running it in the shop at high idle.

Thanks in advance.

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I've got a O ring left over I don't remember taking out. I did some work on my choke knob while the engine was away. Is there an O ring on or inside the choke? I don't see one on the diagram. I think ths slide is in correctly. I've checked and double checked. Thanks.

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Internet communication issue. Did you remove the slide at all,. ever since the last time the bike ran properly?

Describe teh dimensions of the oring. Diameter (ID and OD) Shape (round, tublar or square sectioned).

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I put the bike back together without ever taking the slide out. After I had the starting issues, I did a complete disassemble and reassemble of the carb. So yes, it has been out, but the issues occured before then.

Here are some pictures of the carb and o-ring I had left over. I really don't remember this o-ring, but perhaps my memory is going:excuseme:

IMG_0226.JPG

IMG_0223.JPG

IMG_0222.JPG

IMG_0224.JPG

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I did pull the slide out again to check it and it does have the rubber peice in it.

Also, you'll notice my choke looks a bit strange. It wasn't staying out so I put a zip tie on it and covered it with electrical tape. Fixed the staying out problem.

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The O-Ring looks unfamiliar, never seen one that size on a FCR. It looks more like one that belongs to a oil line fitting.

At this point, There are a few things to check/do.

1) Confirm the tip of the fuel screw is intact and is set correctly (2 or so turns out from gently closed)

2) Replace the pilot jet. Even a 'clean' one can give you grief as the openings in it are so small, it does not take much to make your bike miserable.

3) Make certain you have no vacuum leaks

4) Ensure the hot start is fully closing.

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The O-Ring looks unfamiliar, never seen one that size on a FCR. It looks more like one that belongs to a oil line fitting.

At this point, There are a few things to check/do.

1) Confirm the tip of the fuel screw is intact and is set correctly (2 or so turns out from gently closed)

2) Replace the pilot jet. Even a 'clean' one can give you grief as the openings in it are so small, it does not take much to make your bike miserable.

3) Make certain you have no vacuum leaks

4) Ensure the hot start is fully closing.

Looked a the tip of the fuel screw - I assume this is the same a the air screw right? There is a small narrow tip on it. Looks like it is in good shape. I'll post a picture soon.

I'll get a new pilot on order.

How do you test for vacuum leaks?

How do you ensure the hot start is fully closing except for checking for the cable tension and checking the passage etc.?

Thanks for the guidance. It is greatly appreciated.

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check cam timing.

Did that. timing looks good. Also checked valve clearances and decompression clearances, all within spec.

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Could this be something other than carb related? Something related to the rebuild? All signs point to pilot circut for me, because the bike runs great when at anything off idle, or trying to start it.

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Only simple way to test for a vacuum leak is with the engine running, spray contact cleaner on the carb on spots of potential leaks, if the engine speed changes, there is your leak.

Everything else is as you mentioned. Try starting with the hot start cable disconnected (but the plunger/spring installed.

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great. Headed out now to check for vacuum leaks and disconnect the hot start. I assume the likely places for vacuum leaks are around the in and out boots, and all around the carb? I'm looking for a leaky gasket/seal right?

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Didn't get any response from the vaccum leak test. I used almost all by bottle of carb cleaner. I assume I would have heard the engine rev up a little if I'd of hit a leak. No change in idle, but I do have to have it set at a somewhat high idle, otherwise it just dies immediately.

Hot start was loosened all the way to where the cable has slack, you can hear it thunk inside the carb when opened and closed.

Even after bike is warmed up I'm unable to get any response from trying to kick start. I've tried every combination, choke, hot start, a little fuel, no fuel etc. Doesn't even blip. Hook it up to a tow, get the engine turning over, give it a little fuel and it fires right away.

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Well, thinking logically, if the bike runs great above idle, it is not valve timing or ignition. The only part of the bike that varies on engine speed is the catb. The carb basically has three circuits. Id;e. mid and WOT. Runs fone on mod and WOT. That leaves the idle circut. The idle curcuit has the fuel enricher/choke, this richens the mixture slightly and also adds a little bit of air. It is only needed on cold start. If this were the cause, once heated up, you bike would start and idle fine, so we can rule it out. Other item is the hot start. It only adds air to the mix, to deal with a hot engine that wants a leaner than normal mixture. If it were leaking, the symptoms are those of a vacuum leak. Too lean a mix. You are positive it is working right. The only ither parts of the system is the pilot circuit. This consist of a slow air jet (located in the bell of the carb, on the left side). This can either be a fixed jet size or and an adjustable one. If adjustable, typically it is set between 3/4 and 7/8's of a turn from gently closed. You then have the passageways in the catb leading to the pilot jet then the fuel screw and into the carb. You are positive all these are right.The only other thing that causes no idle issues is if the slide was upside down, as it is supposed to be in in square side down, you are positive that is correct.

For the issue to remain, some part of this was over looked. Does your carb have a coast enricher? Has it been messed with? Any pollution control tubes or cannisters?

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Thanks for the well thought out troubleshoot William1. Tonight I'll go through each of the possibilitilies you identified again and try to find what it is I'm overlooking. I'll also put in a new pilot jet.

How close is a 2008 CRF450R carb to the 2005? My buddy has a 2008 and I'd like to start swaping parts to isolate the problem. I wonder if the carbs are close enough in design to do this.

I'm not sure what a coast enricher is to know if I have one? I don't see any pollution control tubes or cannisters.

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Not being a Honda expert, I could not tell you, but a FCR for the most part, is a FCR. If you pal is up to it, simply swap carbs. If the problem persists, then you know it is not a carb problem.

BTW, also test with the TPS disconnected. Should not make that much of a difference but.....

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