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Discussion Starter #1
Ok guys, this is my first post and it's for a friend whom has a 1980 interstate. I'm also in the market for a wing too but I have a question about my buddies bike.
The bike runs pretty good but a little rough at idle. It was leaking coolant into #1 cylinder but we changed head gaskets and that has stopped. The problem is this and was this even before the head gasket change. I mentioned about the rough idle and after starting the bike and letting it idle for a few minutes you can rest you hand on the # exhaust header and it is only warm where the other 3 are very hot. The spark is good on the #1 cylinder but since it has new plugs I couldn't see if it was getting fuel. Here's the other thing. I checked the compression on all cylinders and2,3,4 read 90 psi and # 1 reads 60. Those numbers seam whacky given the fact the bike appears to perform well, hiiting 100 mph speeds easily and little oil use. I suspect either the guage is whacked or I'm doing it wrong. I do realize that #1 is lower compression than the rest. As far as mileage goes anyones guess is as good as mine. It says 49,000 kms but maybe it has gone around. The bike is fairly clean which leads me to think it hasn't gone around though. Any suggestions?
 

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Something is VERY wrong, either your gauge, your method, the motor, something. 90 PSI sounds low. 60 is QUITE low. I am only guessing, (not a Honda expert but I AM a professional engine builder), but I would think you should have 125 PSI or perhaps a little more cranking. Pull all the plugs, hold the throttle wide open, and with a strong battery, (use jumpers from a running car if you need), crank the motor and let it hit 5 times on the hole with the tester. Use a tester that screws into the plug hole, (12mm 1.25 pitch if I am not mistaken). In your post you just said that # exhaust was cool. I pressume you mean #1. When you test #1 again, do it normally, then give it a squirt or two from an oil can and do it again. That will give you an idea of ring condition. With it having "eaten" antifreeze, they may not be as good as they should. Did you look at the valves, valve seats, guides, etc? Did you check the flatness of the head? You say it runs rough at idle. Try pulling the #1 plug wire off and see if it runs the same at idle.
How did the oil look? Any signs of antifreeze in the oil?
good luck, keep us posted.
Tom
 

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Discussion Starter #3
Yes, I agree, 90 sounds low. Ill try what you suggested because I never took all the plugs out and never held the throttle wide open. One thing is certain. Number 1 is the buggered cylinder. It always gave a puff of white smoke at first fireup and its compression was down compared to the rest. I never checked for flatness of the surface but I did fill all the ports with WD40 which never leaked at all over a day or two. I'll also do the oil squirt and see how that improves things. I did remove the plug wire while idling and it ran the same. The plug appears to have plenty of spark but again, the motor ran the same telling me it isn't firing. I wondered if the low speed curcuit could be block as it pulls good under a load and appears to be ok. If it is running on 3 cylinders I can't wait to see it on 4.
 

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There "could" be a problem with the idle/low speed circuit in the carb, but it can't be ONLY that. When you have some compression, but still low, it is not uncommon to have the hole miss at idle, and make partial power at higher RPM. The WD40 test, while not the best test, is surely good enough to indicate that there is not a real problem with the valves. If you have access to a leak down tester, that would be a good thing to use on #1. Make sure the valves are not too tight. In fact, when you do your comp test, try it with the valves as they are, then with the valves loosened up, even if they are a few thousandths looser than they should be.
Leet me know what you find.
Tom
 

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Discussion Starter #6
Well, I bought the bike off my friend a few days ago and have put 400 miles on it since. Heres the thing. It runs a little rough when leaving a light but once you get on it good and accelerate at wide open throttle it runs much better. Fifth gear at 65 mph, grab a hand full and it runs good. It doesn't run good at steady throttle and no load. I cleaned the carbs, sinced them, set the float height but still the same thing. The compression is 160 psi on 2,3,4, cylinders and 100 psi on #1. The head gasket was leaking a touch into that cylinder in the past so I replaced it. Any ideas guys? Oh ya, at idle if I remove # 1 plug wire the bike idles the same, telling me that it isn't firing on that cylinder at idle or low load. Is it the spark or the compression here? Any suggestions?
 

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Low compression in #1 will keep it from firing. When you get engine speed up, it will fire a little, and is not as noticiable of a miss. If it where me, the first thing I would do is pull the exhaust on that side, and plug a leak down tester in the plug hole. with air being pumped in, the leak down will tell how much it is leaking, (probably a BUNCH), you can then feel/listen at the exhaust port for the leak. In all the THOUSANDS of engines I have machined, I have only seen 1 bad intake valve, so chances are if it is a valve it is the exhaust. Before you lull the head, check the valve gear. Make sure a rocker arm isn't holding the valve open. Infact, I would do the leak down with the gear on, then off, to see if there is any difference. If it still leaks badly, (a good new motor will leak between 1 and 4%), then it has to be either the valves, OR rings. If you have a lot of leakage, and don't hear it out the exhaust, or intake, but in the crank case, then it is probably a broken ring. If the motor ever detonated, that can make rings break. Anyway you look at it, if it is not valve gear, the head has to come off.
One last thought came to mind, when you replaced the head gasket, did you check the head and block for flatness? Also, did you super clean the surfaces to be sure to put the gasket on a very clean, very dry surface? Never use any sealer on a head gasket.
Keep us posted.
Tom
 

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Discussion Starter #8
Thanks a ton Tom. Truth be told is the bike was a goodvfriend of mines just a week ago. I have been involved in helping but a good bit of work was done while I wasn't there. I can't answer for sure about the cleanliness of the gasket surface but I believe it was done with care. Are you saying a broken ring would act similar to a leaky exhaust valve? I was also told that if I put a shot of oil in that cylinder and do a comp test and it comes up than that would point towards broken/stuck rings. I will keep you posted. Like I mentioned, it pulls pretty good under load, hitting 100 mph easily. If it does that on three cylinders while pushing an air pump to boot then I need to experience a proper running version.
 
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