This old bike is getting better, not there yet

[Rettic]

Well tonight I got to take El Six for her fresh spring clean maiden spin around the block. But the problem that I was hoping all this cleaning and polishing would help out, did not. When trying to get the throttle up to redline, she quits accelerating at 6500rpm. It just flat stops. When it does I twist the throttle more and she lurches like she is trying to get on up there to 8500. I can't ever get it to get past 7000.

Now, here is what I have done. Valve lashing, had to do 6 shims. Auto cam chain tensioner, checked timing after install and all is well, no skipped teeth free turning by hand slowly before hitting the starter. Cleaned the carbs with the ultrasonic cleaner. Set float levels to actual fluid levels in the bowls via a modified bowl screw, just below the lock washer. Synced, colortuned, synced again. Did the POR-15 tank treatment, all went well thanks to a 10 buck heat gun at Harbor Freight. Replaced the wire harness, the middle was nicely melted. Checked resistance on the PU Coils, checked fine. Checked the vacuum advance, it checked fine. PU Coil wires intact and withstood pulling hard. PU Coil gap was in spec, if not a little close. Coil wires replaced with new ones as well as all caps. Resistance checked fine after modification. Only thing that I could find off is.... compression on #3. #1 = 182 #2 = 185 #3 = 155 and #4 180. Now, could that be my problem? I have not checked the rings via adding oil to the cylinder. Prob should have. Those numbers are on a cold engine.

Any help gladly appreciated.

[bikerphil]

Did you make sure the mechanical advance is moving freely? If it gets stuck, the timimg won't advance properly. Did you check the timing with a timing light? Yes, you did. One cylinder with slightly lower compression shouldn't cause your problem. You could also do a plug chop at 6K, might be running lean up there. Float height adjustment might be required, and/or larger mains. JAT

[petejw]

I was going to suggest your main jets,
if there to rich the bike will bog down,
but it usually does that around 5000rpm.
Are the butterflies on the carbs opening all
the way?
what main jets are you running?

The low compression on number 3 wouldnt
affect the engine from redlining.

[petejw]

Didnt think of the mechanical advance,
phil makes a good point there.

[Rettic]

I did not think of the mechanical advance either. Correct me if I am wrong, that is the part that is found underneath the PU coils. I will be checking that later this week. As for the mains, Stock 137.5's. Needles are in the middle notch. If that means anything. I did not check timing with a light, just TDC. I don't have a light... need to make a trip to HF for one.

[bikerphil]

Yep, there are springs in there that limit the travel of the weights. Lube up (grease) the mechanism good while you're in there. If you point the reluctor towards 9 o'clock, the P/U coil assembly should come straight off. Make sure the reluctor goes back on the same way, as it can be inadvertently be installed off 180*.

[LoHo]

Might also check the diaphragms in the top of the carbs for pinholes. There are repair tips in the, uh, Repair section.

[Rettic]

Might also check the diaphragms in the top of the carbs for pinholes. There are repair tips in the, uh, Repair section.

The diaphragms are in great shape. The slides drop great, I polished the slide bores. I got to ride her a bit today. Somethings I noticed. At highway speeds she starts to stumble, feels like it is loosing power. Highway being 65+. With the current way it is running it willtop out at 70 on the interstate... sad day. I have not done the mechanical advance check/cleaning. I am also going to be running the checks on the TCI, not sure it is part of it, but worth the try. She pulls great from 1100 to 5500. Just frustrating. Stuck with revs like a Hardly.

[Rettic]

Today's findings

Well I took the time to pull out the mechanical advance and clean it up and re lubricate it with the correct grease. then i put it back together and checked the timing with a light, it was just a degree or 2 off, adjusted that. Checked the PU Coil gap, it was a little loose, so I tightened them. Put it all back together, took it for a spin...... Still crap-tastic from 5000-6500 and it will no go above 6500. I need real help with this, I have been working on the bike all winter, keep changing things and nothing with the way it accelerates changes. I did a throttle chop and found nothing... they plugs were the correct color and all 4 exactly the same. TCI next? Sell the bike? Get mad and throw it out the window? I was hoping it was the carbs, but with the chop it told me that all 4 are getting the right amount of fuel. What else could it be? Anyone close to North Charlotte, NC that could help me out that knows a bit more?

[TopCatGr58]

Other ideas and such.

Hey there Rettic,

Sorry dude, but I'm a bit too far to help...Southeast Virginia!

Okay, let's regroup and summarize! It's a 79SF, you've cleaned the carbs,
(Did you fully disassemble main jets, jet nozzle, etc.? checked the slide vac. diaphragms?)
set float heights, synched, adjusted valve clearances, checked timing chain, tensioner, PU coil wires, New wires/caps on OLD COILS, R&R's the cent. adv., vac. adv working, throttle chop good color all plugs, R&R'd wiring harness, verified elect. timing correct.

Things we don't know, what size are your jets, pilot and MAINS?
Secondly, any other MODS like aftermarket intake/pods vs. OEM Airbox??

You set the float heights with clear TUBES, but what did the actual float heights end up at...25mm, or what??

T.C.

[soccer4m]

try a couple of things

Hi, sounds like some gas starvation under load,,,maybe try
1. running on prime, see how it runs
2. check your fuel filters, inline, for crud
3. squirt some carb cleaner around the rubber carb holders while running to check for any leaks
4. wiggle the pickup wires while running,,maybe stretching under high revs
5. kinked fuel hoses?
6. run some techron fuel cleaner

Hope its one of these,,,,easy to check them all.....good luck, Mike in Sun Diego

[Rasputin]

I agree with TC in that we need to know any mods and which jetting you currently have. The mains could be at fault. I had a similar problem with mine and it required larger main jets. I had installed pods and jardine spaghetti 4 into 2 pipes. It was acting exactly as he is describing his problem. Try a high speed chop and see what you find out from your plug color!

[Rettic]

Answers

Everything on the bike is stock. There are no modifications besides a reusable air filter, UNI brand. The Octy is removed, so there is on, off, and res. I have prime blocked off. As for the jets, once again, all stock. I used a propane torch to try to find a vacuum leak as well, none found. One thing I did try yesterday evening was putting the colortune in and reving the engine up to the offending rpm, and the color was a nice blue. Float heights, before I assembled the carbs to test float level all were set at 25. something, hard to tell exact but all were the same. I then did the fluid test, only one needed adjusting, it ended up being taken down to just under 25 to get it even with the rest. One thing i am going to try today riding to and from work would be to turn on the choke as I am riding to see if it is starvation. As for the carb cleaning its self, I did an ultrasonic cleaning with the carbs completely disassembled. Checked all tiny little holes and they were spotless. Hope this helps. Please refresh me on the number of holes that the emulsion tubes are supposed to have on the inner two carbs, just to make sure I have gotten that right. I believe that I have the fewer holes in the middle two.

[Rettic]

Donno

Well when using full choke under accel, it bogs down. half choke is not so bad, but with out is still better. Still seems to be getting enough fuel. What can the alternator cause problems with, besides charging? The tach will NOT go past 7000k when reved on the stand. Have not checked TCI yet. Still on the list, no non-digital voltmeter. Please advise?

[newc4]

When I cleaned the carbs on my 79SF I thought all the emulsifier tubes were identical, but then again I wasn't paying real close attention on the number of holes.

Darrell