Hesitation from standing stop

I tried to do a search for my issue, but didn't seem to find what I was looking for...so here goes:

Bike has been running well, and most of my ride is at about 55 mph. In the spring I did the shims, colortuned and sync'ed the carbs. New plugs in March.

One Saturday when I was out riding in the rain the bike was hesitating really badly and bogging down on the hills. When I got home I found the clamp for the boot from the airbox was loose on carb 1. I tightened it up and things were pretty good...until today.

Nice sunny day. A good ride. What I noticed was that when getting moving after stopping at an intersection the bike would hesitate when I first let out the clutch, but when the revs got up a bit the bike was happy. I wondered if it was related to my battery, but it is charged, the alternator brushes are good, and it has the correct voltage when the revs are up.

I installed a new clutch cable. Could the adjustment be off and could that cause the problem? It seems to rev OK when it isn't under a load, but maybe the hesitation isn't noticable..I don't know. It seems to be fine when winding up through the gears, just seems to hesitate off the start.

Perhaps there's a vacuum leak that I should test for with propane? Perhaps the petcock isn't functioning at its best? Perhaps I should colortune and sync again before doing something else? Other ideas?

Thanks!

 

I'd definatly check with propane, just to be sure. Why not? Clean your emulsion tubes? Clunk test?
-SLkid

 

Check the plugs and see how lean/rich its running. Pics here if you can.


mn

 

Right lets see a 2500rpm plug chop, it may just need the pilot screws adjusted.

 

I pulled the plugs ang they were all a nice tan. So...I decided to adjust the clutch cable and that seems to have done the trick. Whew.

 

The clutch adjustment wasn't the problem. Went for a long ride on the highway a couple of nights ago and then at a stop light it hesitated again...went back to the drawing board. I found that my vacuum line from the intake boot was cracked and I replaced it. My theory is that that was creating a vacuum leak and caused the rough start. I'll keep you posted, but wanted to report that the clutch adjustment was not the right solution.

 

Vacuum line to the petcock? If so that opens the fuel flow and that would cause strange tings like you have been seeing.

 

Well, I finally *think* this problem is solved. At first I thought it was a loose carb boot, then I thought it was the clutch cable (not...), then I found the cracked vacuum line, but it still ran rough at start and off the stop line. I read in another thread that carefully touching the four header pipes at first start could tell if one cylinder wasn't firing...bingo! Number one was off.

Earlier in the season I tried to check the secondary resistance on my coills, but wasn't having any luck. Probably because I didn't know at the time that one and four are connected and two and three are connected. To make a long story short, the plug cap on number one had no resistance, and once replaced brought things back to life. I had a fantastic ride yesterday.

Diagnostics can be tricky, and I'm by no means an expert, but this board is a wonderful resource. It is a great community that shares experiences and knowledge in a respectful manner.

Have a good weekend, everyone.

 

Cool glad you found it!

 

Cool beans

 

Interesting... I am having the same problems with Rosie. And here is the list of what I eliminated:
Newer tank, no rust, and coated inside.
New petcock.
New 1/4" Motion Pro fuel line,
Cleaned carbs, 3 times!
New coils, plug wires, caps (Thanks Chacal!)
Newer plugs, They are new, but had been carbon fouled because of poor running and diagnosing, but I would clean them up after every run. They are lightly creamed coffee color.
Color tuned and carb synced.

She still hesitates from a stop, but get her in the 3500RPM and higher range and she goes like an ARES X-1 rocket!

TCI messing up the fire?

 

Unless you've got the wrong TCI on your bike, I highly doubt it's the problem. Even if you do have the wrong TCI, I'd still expect problems higher up, rather than down low.

Even though you've cleaned them several times, I still think carbs are the most likely culprit. Not because of dirt or obstruction, but more likely because of jetting, adjustment, or vacuum leaks. I'm assubming that nothing was jamming, that the needles weren't damaged, that the pilot screws and emulsion tubes were in good shape, diaphragms good, etc?

Anything "special" about your bike (exhaust, pods, air filter, altitude, etc) that would require rejetting? Are you sure PO's didn't play mix-n-match with the jets that are in there?

I have a Color Tune and, sorry to say, I wasn't that impressed with it. Yes, it could show the difference between seriously rich and reasonably close to Stoich, but I didn't find it to be all that precise an indicator. I'm also not convinced that it fires the cylinder similarly enough to the correct plug to give me a great indication of what will happen when I put the regular plug back in. I am now in the process of tuning with an Innovate LC-1 Wideband O2 instead. The subtleties of mixture that will pick up on are, at least for me, much more detailed and repeatable.

Anyway, I may well be wrong, but my first bet would be on mixture stabbing too rich or too lean when you're starting off.

Cheers,
Paul

 

The current TCI came from a salvage yard. Pretty sure it was for a 750. Robert is doin' his magic on 2 TCIs that I sent him. Once I get them back, I will know that I have all the correct bits for this model. Previous owners butchered Rosie so bad, I almost didn't buy her to restore.

Ah, here's the thing, this is a separate bank of carbs! I pulled the carbs that came with Rosie. They were a mess! 120 mains????

I bought another bank, that was version correct for Rosie. I have a MAC 4 into 2 and the new coils, so I went up to 112 on the mains, and left everyone else stock.

The carbs that came with her, did not have that cover, over the air jets. Even more interesting, the hole for the screw that holds that plate in place, was not tapped. So on that bank, the covers were not even there!

I see your point about the color tune. I once knew a gearhead who could mix a bank of carbs by sound! We tested him by checking the mileage on a bike before he mixed the air, and after and we picked up 4 miles per gallon after he mixed it by sound!

I do this same kind combination of color tuning and carb syncing on my XS11 Special and she flies!