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Sooty saga follow up

motogtp

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1978 bone stock Super Sport, stock pipes, stock airbox, but Cycle X ignition (just installed). After cleaning the carbs it developed a problem with sooty spark plugs. I got a lot of good advice from the Forum, mostly from Dirt Digger. Charging system good. However, I assumed that the jets were stock 105's. The PO had changed them to 115's for some reason. It runs OK but not great, accelerates hard (thanks Cycle X), and sputters a very tiny bit at steady speed. I have a set of 105 and 110 on order. Do you think that will make a big difference? Start with the 110's or just go to the 105's?
 
I would start with the 105. When you put them in run it good for a couple of miles then go wide open throttle and back off throttle slow...if it picks up power as you roll back on the throttle it is slightly lean and go to the 110. Other alternative that I use is go wide open throttle and start closing the choke...if it picks up power then it is lean. The choke method works at other throttle settings as well to help determine how the fuel mixture is at different throttle openings. You have to hold the throttle steady at the desired opening as you apply the choke or you wont get an accurate feeling of how it is running.
 
I would start with the 105. When you put them in run it good for a couple of miles then go wide open throttle and back off throttle slow...if it picks up power as you roll back on the throttle it is slightly lean and go to the 110. Other alternative that I use is go wide open throttle and start closing the choke...if it picks up power then it is lean. The choke method works at other throttle settings as well to help determine how the fuel mixture is at different throttle openings. You have to hold the throttle steady at the desired opening as you apply the choke or you wont get an accurate feeling of how it is running.

Great advice as always dirt digger. I'm going to hold off on the new floats and Iridium's until I see how the 105 or 110 work. As a side note I noticed earlier that the exhaust pipes are perfectly chrome color still. I don't think this bike has ever run even close to the lean side.
 
I would start with the 105. When you put them in run it good for a couple of miles then go wide open throttle and back off throttle slow...if it picks up power as you roll back on the throttle it is slightly lean and go to the 110. Other alternative that I use is go wide open throttle and start closing the choke...if it picks up power then it is lean. The choke method works at other throttle settings as well to help determine how the fuel mixture is at different throttle openings. You have to hold the throttle steady at the desired opening as you apply the choke or you wont get an accurate feeling of how it is running.

Just thought I would let you know that I think I found the main problem. The float heights were at 25mm, which appears to be the right height for round top carbs, but the Clymer manual indicates that 16mm is the correct height for my keyhole top carbs. I did your float test by dropping them in a can of gas for about an hour. No sinking detected. I now think that the combination of the 115 jets and incorrect float height had me snookered. PO said he had been "all through the carbs". BTW - the manual shows the where the height adjustment for the original brass (round) floats is done. Center of carb, center of float. These floats are a longer, rectangular shape. Is the height measurement still done at the center of the carb or out at the end of the float?
 
Measure on both sides of each float (to make sure they aren't tweaked in any way).


Thanks Stabler. I also found out that the PO had installed them upside down. It's a wonder this thing even ran. Another reason to "never assume".
 
Upside down? Holy cow..

Exactly. That was the reason for the question on where to measure. They were on a severe angle to the float bowl flange. Once installed correctly the floats were nearly parallel to the flange and the measurement was much easier.
 
I can't believe it! I changed the 115 jets back to 105. Flipped the floats back upright and measured 16mm (both sides) float height. Slides and needles are clean as a whistle and move smoothly. The plugs still come out sooty. It starts great with little choke, idles and revs nice. When I ride it has lots of power and very little throttle to move from a stop. After about 3 or 4 miles (in town) though I notice it takes a little more gas to move from a stop. Pretty soon I start losing power until no amount of throttle will keep it moving. After a couple of minutes it starts right up but still has no power. Aaaaaaargh! Just ordered a sync tool so I am starting from scratch. Since the PO put the floats in upside down who knows what else is screwed up. Any other suggestions as I am going through the carbs?
 
Sounds like your losing power in the coils after they get hot, causing plugs to foul (old coils breaking down when hot is a common problem), run it again when it starts to lose power check your spark.
 
Are you using the cycle x coils also? Is it possible you are burning oil? I just noticed your bike is an ss and the F2 motors are bad for wearing out the exhaust guides very fast. Something to look into.
 
What DD and Tracy wrote. You should be sure all else is up to par in your motor BEFORE tearing into your carbs. Many other things can mask as carb issues, while they're in fact not..
 
Are you using the cycle x coils also? Is it possible you are burning oil? I just noticed your bike is an ss and the F2 motors are bad for wearing out the exhaust guides very fast. Something to look into.

Yes, Cycle X coil(s). I don't think I am burning oil, the black soot basically just rubs off. Plus it only has 6,000 miles on it so I wouldn't expect the guides to be gone yet. However, given that I don't know the history of the bike I can't say that the guides aren't an issue.

K2750tracy got me thinking. The weather has been pretty cool and yet the engine seems hot after a 3-5 mile ride. I changed the oil right after I bought it last October and that was 80 miles ago. I changed it last night. It was black, seemed a little runny, and the filter seemed dirty. Is it possible that the oil system is gunked up and not cooling properly? That would explain the slow degradation of the performance. Plus the reason I put in the CycleX ignition is because I lost the coil for 1-4. Knowing that the coil may have failed due to overheating and not age has got me thinking on this differently. Maybe its time to pull the pan and check the pump as well. Would you agree? Thanks for all the help guys.
 
Your running rich issue will cause the oil to thin out and get dirty looking. The dirt oil part is also probably still cleaning out the old oil from the previous owner, you never know how the maintenance or lack of. Hot running engine is from very lean or incorrect ignition and or cam timing. I doubt it is slugged up but its pretty easy to pull the pan.
 
PO lived on a gravel road so I am going to pull the pan and tank just to see. Tonight I drained the crankcase and added about 2 quarts to the tank. It started well and I rode for about 20 blocks with no problem. Let it sit for about 45 minutes and took it out again (10 blocks). By the time I pulled back into the driveway it was just starting to run rough. Popped it into neutral and tried to rev it but it was stumbling. Let it sit for 15 minutes, it started right up and would rev like it had no issues. This thing is kicking my ass. As a side note, should the engine serial number and frame number match? Frame SN is 750F-******* and engine SN is 750E-*******.
 
No serial numbers do not match. Did you get the cycle x ignition with the single coil pack or the 4 individual coils? Might be time to pick Kens brain and ask some troubleshooting questions. If you had a working stock ignition system with coils I would say swap back to stock and see if the problem stays or goes away...then you could eliminate ignition as the problem.
 
No serial numbers do not match. Did you get the cycle x ignition with the single coil pack or the 4 individual coils? Might be time to pick Kens brain and ask some troubleshooting questions. If you had a working stock ignition system with coils I would say swap back to stock and see if the problem stays or goes away...then you could eliminate ignition as the problem.

Got the single coil pack. Funny, I was thinking about calling Ken as well. Plan is to pull the pan to look for crud, tune the carbs, and do a couple of quick oil/filter changes to flush the oil system. The fact that the jets were 2 sizes too big, the floats were installed upside down, and the air box was missing a bolt (so one side open slightly) has me wondering how much the PO messed this thing up. I got a good reference for a local motorcycle mechanic so that is my fall back plan.
 
I would try a fresh set of plugs also if you haven't done so already. Extremely rich will foul the plugs and sometimes you will never get them to fire reliably after they have been hard fuel fouled.
 

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