79 runability problem.

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NobleHops
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Re: 79 runability problem.

Post by NobleHops »

Straying out of my depth perhaps, but are you certain you have all OEM float valves? Or at least all the same? If you haven't already, you might try the clear tube test, see what the fuel levels are without relying on measured float heights. If you had a couple of rogue needle valves in the mix it might mislead you if you were trying to tune these carbs by the book.
Nils Menten
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Re: 79 runability problem.

Post by daves79x »

As everyone here knows, I'm the LAST guy to say it's not the carbs, 'cause it usually is, but don't think so here. Try the coil swap test if your carb tune-up doesn't work.

Dave

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Re: 79 runability problem.

Post by Gearheadgregg »

damn Ethanol gas...make sure you check the O-rings also on the mixture adjustment screws spring washer, try and heat the $hit out of the slow jets with a torch and burn them clean, i have had to replace them before because i could not clear them out..also you said after you let it cool down a while it would act up more..usually a cold motor will require more fuel and will missfire if partially plugged, no secrete these are Lean from the factory already to pass EPA , surprised they run at all with the jetting ? if it does it again do the Old school check at first startup and running tap the pipes with your finger find the cold ones..the check spark on that cold cylinder. cold with good spark would point to carb jet issue

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Re: 79 runability problem.

Post by Gearheadgregg »

[quote="Gearheadgregg"] also check for vacuum leaks around carb insulators

whatscooking
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Re: 79 runability problem.

Post by whatscooking »

I have swapped coils, got both of my automotive spark testers out, standard and HEI, it throws a good 1\4 spark on every one. Last night when I was spraying cleaner through the idle jets I found it interesting the different distance between the jets on how far I could shoot a stream. Clearly two of them fell short. Just guessing on the distance but the best ones would shoot 12-14 feet, two of them would do good to make it 9-10 feet clearly less fuel going through them and I did find one that only made it 2 foot.
Is there anyplace I can get correct needle valves for the float. I can get the complete Honda valve and seat for $31.00. I am on PJ Motorsports web and they have what they say are oem but I want to make sure these are correct 018-880

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Re: 79 runability problem.

Post by whatscooking »

Just checked on the jets after their overnight soak. But first I got out my little 40 power magnifier to look at the tapped end of the jet. The first time I did them I took them out and looked at them with my glasses and used a piece of emery cloth to shin them up,,,,,,,,,,,, I thought. What a train wreck there is in there, got my little electric tool and pic and got that looking lots better this time. Especially when you drive them in if anything is hanging there it would be instant problems. Also I checked the distance this time when I spray through the jet with brake cleaner. I now can spray and hit a piece of wood that is beside my wood stove that is a full 15 feet away, what is neat by the time I get another jet hooked up the cleaner has evaporated off the stick of wood so I know it hits.

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Re: 79 runability problem.

Post by daves79x »

These are OEM needles only - everyone save this - it's been posted many times: http://www.pjmotorsports.com/keihin-mik ... tml#Keihin Needle assy

If you need just the float valves, they are the real thing for way less than the Honda needle/seat combo.

Dave

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Re: 79 runability problem.

Post by daves79x »

About the coils - static testing is OK, but actually running them is sometimes a different matter. If your carb tinkering does not net any results, see if another pair of cylinders soots up with the coil swap.

Dave

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Re: 79 runability problem.

Post by whatscooking »

Needle valves ordered, all the brass cleaned, checked\rechecked, installed in carb.

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Re: 79 runability problem.

Post by whatscooking »

Carbs back together and on with the same results. I spent the day swapping to the original air filter set up and taking even more disc out of the Super Trapp no difference. I took the complete coil\wire set up off another bike and tried it with no difference. I spent some time checking the spark advance with a timing light and I can see it moving with RMP change. It has 422 stamped on it.
The only option I have left, as I see it, is to change out the carb with the other 79 I have in my shop, not that I want two bikes torn down at the same time but I have run out of ideas.

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Re: 79 runability problem.

Post by NobleHops »

What about the spark plugs themselves? Have those been eliminated as a possibility? You've certainly tried every other possible thing.
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Re: 79 runability problem.

Post by whatscooking »

NobleHops wrote:What about the spark plugs themselves? Have those been eliminated as a possibility? You've certainly tried every other possible thing.
I am on my third set of NGK DR8EA plugs. The crazy thing about this is I can go out there right now on a cold start up, and it will fire right up, I can take off and it operates fine, no bucking, ride it normal ill say five miles or so and it will start in. If any of you have been out of Madison on 421 from the Ohio river nice long steep hill four lane with a guardrail between, cop on other side, I can run her 70-80 pulling uphill real strong and when I get to the top of the hill to head back home and then go slow\steady around that 2000 RPM no hint of this bucking for a mile or so then back it creeps into it's fit throwing. I have tried to see if the choke will bring it out and somewhat sorta it does but like I said if you keep a load on the engine or get it up above 3000 RPM things are fine anyway. I have thought about the cam chains slapping around could cause this but everyone says I would hear that and when I had my timing light on it the advancement looked to be smooth, I did adjust them.

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Re: 79 runability problem.

Post by Goss »

If I was a gambling man I would put my money on the coils/ignition.

viewtopic.php?f=20&t=6970&hilit=misfire

These symptoms look similar to me.

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Goss
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Bike http://www.youtube.com/watch?v=ofjFhEd3

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Re: 79 runability problem.

Post by whatscooking »

I read that thread a little while back and went out to look things over. I went as far as taking my soap mister bottle and wetted the coil area real good and with the lights off and then bare handed couldn't find spark escaping believe me I tried. I have swapped the Dyna ignition module and the coil pack and wires and ran a hot wire directly off of the battery to run the coils. I do have a concern when they were talking about the advancer getting weak. If it is getting advance too quick and then pulling back I could see where that could make one buck but when I was watching with my timing light the movement seemed to smooth not jerky.

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Re: 79 runability problem.

Post by Larry Zimmer »

Hot coil break-down is an internal thing. You won't be able to find anything wrong externally. Even when operating. The only diagnostic is to replace suspect coil(s) with a KNOWN good coil. (Not necessarily new -- just known good. I've seen new be bad.) Then, do the same riding as produced the problem. If it is the coil(s), problem will be gone. (Same thing can happen with cars. Ask me how I know.)
Larry Zimmer
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