Author Topic: Skipping when coasting slowly? (Read 1834 times)

robdrobd · « **on:** August 29, 2011, 04:48:50 PM »

Tonight after a short 15 minute ride I turned into my development and dropped the bike into 2nd (1976 750k) gear and it started skipping and misfiring. The last few times I've gone riding I can not "coast" in a low gear without this happening. Is this a timing issue?

robdrobd · « **Reply #1 on:** August 29, 2011, 06:07:06 PM »

Pulled plugs, they seem fine.

BobbyR · « **Reply #2 on:** August 29, 2011, 06:08:50 PM »

Have you pulled the carbs and checked the emulsion tubes and slow jets?

bollingball · « **Reply #3 on:** August 29, 2011, 06:12:31 PM »

When were the carbs cleaned? were the slow jets removed and cleaned
Does it run well at high speed? When was the 3000 mile tune up done last.

robdrobd · « **Reply #4 on:** August 29, 2011, 06:16:19 PM »

Carbs have been cleaned and it runs well when I give it any throttle. Has great response. It just skips when coasting at about 20mph or lower when I'm not giving it gas and trying to coast at really low speeds. Could it be a condenser?

BobbyR · « **Reply #5 on:** August 29, 2011, 06:37:50 PM »

What is your idle speed, sounds like it may be bucking.

robdrobd · « **Reply #6 on:** August 29, 2011, 06:47:26 PM »

What exactly is bucking? Maybe it's bucking instead of skipping

My idle speed is 1400

robdrobd · « **Reply #7 on:** August 29, 2011, 08:06:13 PM »

Randy · « **Reply #8 on:** August 29, 2011, 09:37:41 PM »

My 500k does the same... It sounds and feels like a cylinder is droping off.. And once you get on it..The sound and feel goes away... I'm running a 4 into 1 mac with pods.. It could be back pressure in the pipes..

Zodo · « **Reply #9 on:** August 29, 2011, 10:50:30 PM »

Just speaking from my experience with PD series carbs (not sure how different your carbs are) could one or more air cutoff valves not be working properly? I would pull the carbs and take a look at the diaphragms and o rings as well as the little air hole that the o ring protects...make sure it's clear.

robdrobd · « **Reply #10 on:** August 30, 2011, 05:00:55 AM »

I am running a Mac 4 into 1 with stacks. How would I solve a back pressure problem?

robdrobd · « **Reply #11 on:** August 30, 2011, 05:51:50 AM »

Too much or too little back pressure, and how do I solve it?

robdrobd · « **Reply #12 on:** August 30, 2011, 09:38:18 AM »

I am going to check the timing and condensers and see they jive.

florence · « **Reply #13 on:** August 30, 2011, 09:43:04 AM »

I have a laser 4-1 which is tiny and has very little back pressure - no problems, ticks over (idles) fine.

BobbyR · « **Reply #14 on:** August 30, 2011, 09:51:37 AM »

Quote from: robdrobd on August 30, 2011, 05:00:55 AM

I am running a Mac 4 into 1 with stacks. How would I solve a back pressure problem?

With and open exhaust and stacks you are probably running real lean at idle and just above.

florence · « **Reply #15 on:** August 30, 2011, 09:54:25 AM »

Using bigger jets helps.

robdrobd · « **Reply #16 on:** August 30, 2011, 10:03:32 AM »

I swapped to 105's for 120's. Maybe I will turn the airscrews all the way in and see if it helps. Would a bad condenser cause skipping?

Zodo · « **Reply #17 on:** August 30, 2011, 06:25:09 PM »

At low, coasting throttle, you're going to be relying on your idle jets, not the mains (that you changed to 120).

robdrobd · « **Reply #18 on:** August 30, 2011, 07:27:34 PM »

Do you think with stacks I need to up the idle jets as well?

Zodo · « **Reply #19 on:** August 30, 2011, 08:01:42 PM »

Most definitely. There is more air and lower vacuum across the board, so you'll probably need to bump up your idle jets at least two sizes.

robdrobd · « **Reply #20 on:** August 30, 2011, 08:42:49 PM »

My idles are stock #40's. Should I jump up to 45's. Better to be rich than lean

BobbyR · « **Reply #21 on:** August 31, 2011, 09:41:16 AM »

If you are lean at idle, have you tried a bit of choke to see if that helps. If it does you are lean.

robdrobd · « **Reply #22 on:** August 31, 2011, 10:49:14 AM »

Choke kills it so I don't think it's too lean. While thinking about it I adjusted the cam chain tensioner though

That quieted the bike down a bit.

camelman · « **Reply #23 on:** August 31, 2011, 12:21:42 PM »

Your engine is bucking at idle settings (throttle closed runs your carbs at idle settings regardless of rpm), which corresponds to your mixture needle. Check your needle settings to see if all cylinders are set the same. If not, then adjust them to factory specs. If that doesn't help, then try going in/out 1/4 turn at a time (on all at the same time) to see if the bucking gets better or worse.

robdrobd · « **Reply #24 on:** August 31, 2011, 03:30:38 PM »

Ok, right now they are at 1/2 turn out. I will put them at 1 and 1/8 and work my way down.

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Author Topic: Skipping when coasting slowly? (Read 1834 times)

bollingball