plugs fouling

[untill62]

I sure hope someone has a remedy to my issue. I was really looking forward to some riding, but I can't seem to go 10 miles on new plugs(D7ES), new gas, new air filter,cleaned out carbs and tried to do everything the carbon fouling problem mentions. I still end up with black carbon plugs. Runs pretty good over 3000 rpm, but below it's sputters and runs like 3 cylinder. The slow running jet is marked 40. I mentioning that just in case that would be an issue. But that is the stock jet as far as I know. I am the second owner and I know nothing has been modified. I did have the cylinder lightly honed and put in new rings and probably haven't put on 100 miles since doing it.
Every year I have to clean out the jets with a small wire to get all the cylinders firing.
I just want to have a month of running great and not 10 miles??
I hope you guys can help. Thanks

 

[Dave]

Cleaning jets with a wire ruins them. Replace any jets you stuck a wire in.

If your leaving it stored for most of the year you need to drain the carbs, gas tank, and crankcase before you store it for the year.

 

[untill62]

Cleaning jets with a wire ruins them. Replace any jets you stuck a wire in.

If your leaving it stored for most of the year you need to drain the carbs, gas tank, and crankcase before you store it for the year.

I ordered new jets and filters for the fuel lines. Will try it again and see if I can stop the fouling plugs. Maybe electronic ignition also.

 

[madmtnmotors]

I ordered new jets and filters for the fuel lines. Will try it again and see if I can stop the fouling plugs. Maybe electronic ignition also.

What bike?

Forget the electronic ignition for now. Get it right first, otherwise you are introducing new variables. Carbon fouling is a result of over rich fuel/air ratio.

 

[untill62]

What bike?

Forget the electronic ignition for now. Get it right first, otherwise you are introducing new variables. Carbon fouling is a result of over rich fuel/air ratio.

I was thinking that before electronic ignition, we would do something else. Do you thinks coils could also be a problem?
So after putting in the new jets new plugs, how do I change the fuel/air ratio. I don't have carb adj. screws.(1974 750). I do use carb synchronizing tool(lead in tubes). I have had problems with this for a very long time, so I guess there must be a carb adjustment I am not doing right?? thanks

 

[dirtdigger]

There are idle screws on the carbs if they are stock. Idle jet does lower throttle openings, needle height adjustment does part throttle through 3/4 throttle and main jet is mostly a wide open throttle adjustment. I use the choke a lot for diagnosing jetting issues. When you get to the trouble spot you are trying to fix...start to slowly close the choke...if it gets better it is lean, if it gets worse and bogs down then it is rich. No matter what you do you need to start with a sound motor...good compression, valves and timing chain adjusted, good points and condensor, correct timing and dwell, no air leaks at the carb boots, clean air filters.

 

[untill62]

There are idle screws on the carbs if they are stock. Idle jet does lower throttle openings, needle height adjustment does part throttle through 3/4 throttle and main jet is mostly a wide open throttle adjustment. I use the choke a lot for diagnosing jetting issues. When you get to the trouble spot you are trying to fix...start to slowly close the choke...if it gets better it is lean, if it gets worse and bogs down then it is rich. No matter what you do you need to start with a sound motor...good compression, valves and timing chain adjusted, good points and condensor, correct timing and dwell, no air leaks at the carb boots, clean air filters.

You are saying idle screw. I have 3 manuals and none have a reference to idle screw. Is that the same as the air screw(what I use to sync carbs with my sync. tool,(mercury gauges)?) I have no other adjustments other than carb operating rods on top. I also do not have, what the manuals are calling "throttle stop screw" on side of carb where air screw is. I have 3 manuals and they all show that screw, but not on my bike. I am second owner and have had it since 1975, so original carbs.

 

[dirtdigger]

The air screws on the side of the carbs are not used for syncing the carbs. The rods on the top of the carbs at the throttle linkage are what you use to sync the carbs. The throttle stop screws were only used on the very early carbs that had 4 individual throttle cables thus each carb had its own throttle stop. Your carbs will have one throttle screw in the middle of the rack on the linkage. If you have been using the screws on the side of the carbs for syncing then all you have been doing is messing up the idle mixture.

 

[untill62]

The air screws on the side of the carbs are not used for syncing the carbs. The rods on the top of the carbs at the throttle linkage are what you use to sync the carbs. The throttle stop screws were only used on the very early carbs that had 4 individual throttle cables thus each carb had its own throttle stop. Your carbs will have one throttle screw in the middle of the rack on the linkage. If you have been using the screws on the side of the carbs for syncing then all you have been doing is messing up the idle mixture.

I'm confused since both the Haynes manual and the Honda shop manual talk about the final adjustment to be made with the (pilot jet screw-Haynes description) or (air screw-Honda shop manual description). They each have a different name for it. Both say first to adjust the cable adjuster at top of carb with vacuum gauges attached so all read about the same, but both have different cm values. Can I make those same adjustment with my mercury gauge?
The Haynes manual says for the initial adjustment on the pilot jet screw to be 3/4-1-1/4 out and the Honda shop manual says 1 turn out, so about the same.
By the way I really appreciate you taking the time with this!!

 

[madmtnmotors]

The air screws on the side of the carbs are not used for syncing the carbs. The rods on the top of the carbs at the throttle linkage are what you use to sync the carbs. The throttle stop screws were only used on the very early carbs that had 4 individual throttle cables thus each carb had its own throttle stop. Your carbs will have one throttle screw in the middle of the rack on the linkage. If you have been using the screws on the side of the carbs for syncing then all you have been doing is messing up the idle mixture.

+1

Air/fuel is affected by many things:

>Float height
>Main jet needle position (has more affect on mixture at higher rpms)
>Vacuum leaks (affects mixture at all rpms)
>Main jet size (affects mixture at higher rpms)
>Air screw settings (affects mixture mostly at lower rpms)
>Air filter (clogged air filter will create a lean condition)

Carbs suck. Start with stock setup for the carbs to establish a baseline. Stock air filter, stock jet sizes, stock needle position, stock float height, stock settings for air screw (idle mixture) and go from there. Sync the carbs properly as described in the manual. These bikes were designed to run properly with these settings.

Then make sure the ignition is timed and firing properly. If the carbs are setup properly these bikes will run on two cylinders. It won't run very well, and it won't have much power, but it will run.

Since you have to "clean the jets" every year, I would start with a complete teardown and rebuild of the carbs. Clean the fuel tank and petcock while you're at it. As for carb kits, make sure the rubber parts are "Viton" if you go the aftermarket route, or use original Honda parts.

 

[untill62]

I'm confused since both the Haynes manual and the Honda shop manual talk about the final adjustment to be made with the (pilot jet screw-Haynes description) or (air screw-Honda shop manual description). They each have a different name for it. Both say first to adjust the cable adjuster at top of carb with vacuum gauges attached so all read about the same, but both have different cm values. Can I make those same adjustment with my mercury gauge?
The Haynes manual says for the initial adjustment on the pilot jet screw to be 3/4-1-1/4 out and the Honda shop manual says 1 turn out, so about the same.
By the way I really appreciate you taking the time with this!!

I have a 3rd manual by Clymer and they do not have a final adjustment for the air screw, just 1 turn out and then adjust the throttle rod to raise or lower vacuum. Interesting

 

[dirtdigger]

Haynes manual sucks, and it sounds like you have the very old edition of the honda manual. The adjustment you are describing is for the early carbs with four cables and you do adjust the cables on those, but the carbs you have should not have a cable on each carb...there is a linkage that operates all four carbs on yours correct? Maybe you should post a picture of your carbs so we can determine if we are talking about the same things. It sounds like either your manuals are for the early bikes or you have the wrong carbs on your bike. The air screw adjustment and carb syncing are two totally different things.

 

[untill62]

I replied on a different thread but will again here dirtdigger. Thanks for all the feedback. I do have the carbs you were describing, with a carb rail, 2 throttle cables in middle and the throttle stop knob.
I did buy new slow jets(40), new plugs(D7EA), new air filter, inline fuel filters. I took out the four idle air screws and put in carb cleaner and put back in to gently seat, then back out 1 turn and will leave them alone now. They were all in different positions. But all the plugs were fouled when I replaced them.
I have not synchronized carbs yet. They now about 1 thread above the lock nut. I didn't think I would try to synch carbs until I put on 15 miles to see if plugs foul. Doesn't seem like I should have to other than to make it run more smoothly, but the fouling of plugs is my first goal. Should I have bought new main jets? I would just buy rebuild kits, if I needed to do that. I have pull the carbs off a few times in its history, but now know I was not doing the synchronizing correctly because of the idle air screw I was moving whiling synchronizing.
Thanks

 

[dirtdigger]

Put the new plugs and jets in and see how it runs. Have you set the float levels correctly? This can also have a large effect on fuel mixtures. Normally not so much at idle unless they are very high or very low.

 

[untill62]

The floats are all pretty close to the 26MM when just touching the float valve and not compressing the spring. Started it and runs great with great throttle response. It's not a nice even pur at 1000rpm, but hit the throttle a little and instant response. So I guess now just take it on a ride and see what happens?

 

[dirtdigger]

The idle will be a lot smoother when you get the carbs synced properly, that is the biggest contributor to idle quality on the 750. I would take it out and run it.

 

[untill62]

Well I did take it out for about 15 miles, not over 60mph. I pulled the plugs and No 1 was about 1/4 carboned, no 2 & 3 about 1/2 was carboned (1/2 black and 1/2 white). And no 4 fully black. So I don't know what is going on? What about what someone said about the coils or electronic ignition? Any ideas?

 

[Dave]

I'm a pretty good mechanic. I can tear down and rebuild just about anything. I've got a full craftsman/snap-on roll away, a full set of air tools, and several other small tool boxes. I can degree cams and scan your new honda civic but I do not have a gauge set for synchronizing carburetors nor any experience doing it.

I take it to a small shop that has several old motorcycles for sale out front and an old white bearded mechanic in back for that.

That being said I do everything else myself. Adjust the valves (be thankful you have a SOHC), tension the timing chain, check the rubber intakes for leaks. I hope your running an air box and not pods, you never mentioned which. Get brass floats if you have plastic ones.

Check the timing. You do this just like an old car, by pointing a timing light at the marks. If it's jumping around your advance mechanism is worn out. Dual points are a bitch but doable if you buy the original (expensive) parts. Honda condensers will make you cry but aftermarket ones are garbage and you can get the pamco electronic for about the same price as rebuilding the stock ignition with genuine Honda parts.

Check your spark at the plug. Get a spare spark plug and plug it in and use jumper cables to hold the plug (small ones or even jump starting ones if that's all you got) and connect it to a spot on the motor (or hold the plug against the valve cover with your hand grasping it by the plug cap if your not afraid of getting shocked).

If you see a small thin spark, your ignition has issues. You want to see a bright spark as wide as the ground electrode.

I also have a 74 and I also used to foul plugs regularly. I carried spares with me so I could change them on the side of the road. I finally replaced the entire ignition system, pamco electronic, coils, and plug caps and haven't fouled a plug since.

If your going to do it anyways, it may make the rest easier as that's one variable removed.

 

[untill62]

I'm a pretty good mechanic. I can tear down and rebuild just about anything. I've got a full craftsman/snap-on roll away, a full set of air tools, and several other small tool boxes. I can degree cams and scan your new honda civic but I do not have a gauge set for synchronizing carburetors nor any experience doing it.

I take it to a small shop that has several old motorcycles for sale out front and an old white bearded mechanic in back for that.

That being said I do everything else myself. Adjust the valves (be thankful you have a SOHC), tension the timing chain, check the rubber intakes for leaks. I hope your running an air box and not pods, you never mentioned which. Get brass floats if you have plastic ones.

Check the timing. You do this just like an old car, by pointing a timing light at the marks. If it's jumping around your advance mechanism is worn out. Dual points are a bitch but doable if you buy the original (expensive) parts. Honda condensers will make you cry but aftermarket ones are garbage and you can get the pamco electronic for about the same price as rebuilding the stock ignition with genuine Honda parts.

Check your spark at the plug. Get a spare spark plug and plug it in and use jumper cables to hold the plug (small ones or even jump starting ones if that's all you got) and connect it to a spot on the motor (or hold the plug against the valve cover with your hand grasping it by the plug cap if your not afraid of getting shocked).

If you see a small thin spark, your ignition has issues. You want to see a bright spark as wide as the ground electrode.

I also have a 74 and I also used to foul plugs regularly. I carried spares with me so I could change them on the side of the road. I finally replaced the entire ignition system, pamco electronic, coils, and plug caps and haven't fouled a plug since.

If your going to do it anyways, it may make the rest easier as that's one variable removed.

I do have some work to do. I am tired of this, but will check out the things you mentioned

 

[untill62]

Fouling plugs, I still have. I am back after a couple years. I had some med issues, but decided this year to try again with my 74, 750. so this is a continuation of the above discussions. So I took the carbs off, cleaned them, new plugs, new coils, new electronic ignition, new boots. Timed it at 2500rpm as per a discussion on a forum. And back to the same!!! Plugs carbon up after 10 min of running
I had a detached retina and wanted to buy an ST1300, but thought I would ride my 750 to see if my vision gives me any trouble. so am wanted to get at this again.
I think i'll check compression, but I suspect it will be fine. Also maybe replace the boots between carbs and engine. I did try to soften them, but still pretty hard. Would that cause any of this?
Oh, and also took off tank cleaned it out and used new, with no ethynol premium, plus added octane booster from amsoil. Seems I have covered a lot of bases??