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Pipe glowing red! Help Honda Mechanic!

23760 Views 19 Replies 8 Participants Last post by  buckcrazy
I have a 95 foreman. I purchased it with the motor in a box. It used to have a 500cc piston and cylinder kit but I have replaced it with a stock cylinder and piston. I have replaced the hot cam with stock. I have rebuilt the carb with stock jetting. It has a honda stock airfilter with box and snorkle and stock exhaust. I have lapped the valves and installed new stem seals. I have adjusted the valve clearance to book values. Compression and leak down test good. Timing appears right on. I have taken it to two reputable shops and both failed to fix. It will start easy but quickly turns the exhaust pipe red and "coughs or spits" out the carb one out of every five times it fires at idle. Eventually, it will "cough" hard enough to stall. It does the same thing with or without the muffler. The head pipe is clear. Any suggestions?
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I'm not HM, but he may have a better ideal on what is causing this problem. the only thing I see you didn't mention was what the needle position and air/fuel mixture is set at. The needle is usually set from the factory in the middle grove and air fuel mixture is around 2-2.5 turns out.
The exhaust turning red is usually a sign that the bike is running lean. Possibly the carb tuning as Dirty has suggested or even a problem with the carb rebuild. Good luck and keep us posted.
Thanks for your reply! The needle is set in the middle and the air screw is set about 2. I have tried adjusting it with no change. I asked the previous owner why he had it apart and he said he thought it jumped time. It makes me wonder if it had the same problem before and that is why he took it apart. The reason I returned it back to stock is because he broke a small piece off the skirt of the 500cc piston. The Honda shop I took it two suggested I check the flywheel key to see if it is loose, does this make any sense?
Hello H4! Thanks for your reply! I agree, part of the reason I rebuilt the carb and made sure it had the correct needle and jets. I have soaked the carb, ran fine wire and compressed through all the passages. The mechanic at the one shop had the foreman for two weeks. He tore the carb off a couple of times and couldn't find anything wrong either. In fact, when he finally gave up, he refused to charge me anything. He was totally stumped.
What factory jet did you install, was it the 125 or 130?
I installed the 130. I am at about 600ft above sea level.
There are a number things that can cause the engine/exhaust to run hot .. Partly plugged exhaust , tight valves , lean carb , wrong/loose spark plug , ICM.. When the engine was changed back to 400 it will run hot until the new parts break in but it shouldn't run hot enough to turn the header pipe red .. Does the bike work good besides the exhaust turning red ..?
I've seen a few Honda's (including my own 500 ) where the head pipe gets red hot....I've really never worried about it.
HM, Thanks for your reply.

No, when cold and initial start it ins't too bad for the first 30 seconds or so, then it starts to cough back through the carb and won't rev up worth a ****. It then starts to sound like its detonating a little with the header pipe truning red and i shut it off. It really appears to be something with the carb but I've had it apart a dozen times and so has one of the shops I've taken it too. If at idle, won't it only use the idle circuit in the carb? Could it be plugged? I've run thin wire and compressed air and soaked it with no change.

I've tried running it with just the header and it still turns red. I've tried it with no filter or box or snorkel and still red. The local honda shop looked at it and told me it needed to be rejetted and or they thought the flywheel might be loose. I have owned many honda's in my time, fixed numerous others and have never had a problem like this that i can't fix. It's very frustrating.

Since it seems so much like carburetion, I put a carburetor from another good running 400 onto this troubled one. Guess what? Same problem.
Joe it looks like we're running out of options. My next step would be to pull the front clutch cover and verifly the timming by the cam and flywheel T mark. then recheck the valve clearance (.006") Something is fishy somewhere and it doesn't make since.
my 400 pipe turns red but iv neer actually paid close attention to it , but i do use the red pipes to warm my hands in the winter
QUOTE ("jer400":2eecxgsf)
my 400 pipe turns red but iv neer actually paid close attention to it , but i do use the red pipes to warm my hands in the winter
HA! I've done the same thing! Works pretty good for that.

I've been on the road (job) for the last 10 days and haven't had a chance to do anything yet. Let me ask you this, if I remember right, when I installed the new cam, there are dots on each gear that you need to align. Is this correct? Should I be looking at the ignition timing mark as well?

I do believe there is something wrong with this motor internally.
yes there is a dot on the cam and cam sprocket to make sure it is put on correct, align the dot with the mark on the casing just above the cam sprocket, remove the inspection plug on the right side of the engine and use the T mark on the flywheel to set the timming.
I have the manual that I will reference. Is there a website or another source that I could reference as well?
i know this is old but did you ever fix it i am having the exact same problem i just totaly rebuilt the motor this thing is driving me crazy
does your's have a o ring between the boot and the head mine was left out after a repair and it ran lean and we wore out the carb befor i found it. no nothing me.
it does have the o ring i put it in second before putting the boot on
i have sprayed carb cleaner around everything including head cant find no leaks
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