Weird low rpm problem

[dbeardslee]

So last week I installed new main and pilot jets. It was still a little soft on the bottom, so I lowered the floats (installed position) by a 'heavy' mm and resynched. She was running perfect. I put several hundred miles on this setup with great results.

Then yesterday I took a run down to a friends house, and towards the end of the ride she was really rough at idle - missing, popping back through the carbs, and generally not wanting to idle. I got her back home and pulled the plugs to see which carb might have been giving me trouble, and they were all perfect - no fouling and a nice medium brown color across the board.

I put my synch gauges on her, and they were really doing a dance - the readings were fluctuating wildly. Made me suspect a vacuum leak, but disconnecting the vacuum advance and plugging (at the carb) and spraying the carb boots with WD yielded nothing. I started thinking TCI, so I removed the connectors, cleaned the old dielectric out and reconnected them dry. Problem seemed a little better, but still not right.

I also gave her a dose of seafoam yesterday, just in case I sucked something into the carbs, but haven't fired her up yet today.

The problem is only in the very low rpm range - 1000-1500 or so. I thought I might have a problem in the pilot/enricher circuit, but after intentionally putting around a low rpms my plugs still look perfect across the board. So anybody got any ideas where to look for a solution?

[DenyP]

It sounds like some crud in the pilots to me. Let us know what the sea foam does for ya.

Deny

[TopCatGr58]

Hey DBeardslee,

You've got a standard, the petcocks are vacuum controlled. Sounds like it was possibly running out of fuel? A crack in the petcock vacuum line to the intake boots could cause both a vacuum leak, and fuel flow problems due to insufficient vacuum to properly open the petcock valves all the way to allow for good fuel flow.

Regrettably, I can't remember, but I think the Standards also have a PRIME petcock function/position, could try turning it to that to see what happens.
JAT!?
T.C.

[dbeardslee]

TC - I got rid of the vacuum petcocks and replaced with manuals, but your right - it's acting like it does when it's running out of gas.

I'm thinkin' crud in the pilots is a good place to start. Was also thinking that maybe one of the pilots wiggled loose? The seafoam seemed to have helped a little, but it still isnt' right. I think maybe the carbs ingested something through the vent lines. I can't remember exactly but it seems like I heard a little pop just before it started running rough.

The thing that has me confused is the condition of the plugs - they're perfect. I don't know, maybe because I've had to keep on the throttle for it to idle right it didn't foul them, but I did do a fair amount of sub 2k putting and they're still clean. I'll pull them and post back what I find.

[dbeardslee]

This just in...

I took the carbs off, and cleaned the pilot circuit, the mains, and everything else on the bottom of the carbs. One thing I noticed was that when I put compressed air through the #3 carb main jet tower (jet removed) the emulsion tube moved down. I took a long screwdrive and moved it back up where it's supposed to be, and it looked like it was on the same level as the other tubes. Seems to me like they only go in one way, but it's been a long time since I had them out.

Anyway, I put them back together and cranked her up and took a ride around the block to warm her up. I could feel the problem when it was cold but not very pronounced at all. When she fully warmed up I got the same problem. Brought her back to the man cave and put the synch gauges on her. She keeps farting through the #3 carb, and I noticed that the vacuum gauge I had on #3 would look good for a while, and then the vacuum would drop by about 5" and then come back up. The vacuum on the other carbs was jumping around a little, but that seemed to be driven by good old #3. I'm thinking I may have a vacuum leak somewhere in #3 - possibly the boot (although spraying WD40 around it yielded no change).

Other thoughts?

[dbeardslee]

One item I forgot to mention...

Once she gets past 2500k she runs like a scalded dog.

Also this question - I installed pod filters last year. Has anyone had a problem with carb boots leaking after installation of pods? Without the support from the airbox, all the weight is supported by the carb boots, so I just thought I would ask.

[Crazcnuk]

The emulsion tubes are held in by the main jet. When you take the mains out you can take the tubes out and soak them as well.

There is a pin in the tube bore so they only go one way.

Have you tried turning the mixture screws out a little? Maybe your running too lean at idle now?

The vacuum readings always fluctuate wildly, that's why there are damper screws on the synch guages, so you can turn down the flutter.

[dbeardslee]

Craz - I've got needle valve dampers on the lines so I can watch the gauges with a pretty high degree of accuracy, and I always make sure they move just a tiny bit so I know I don't have them shut completely off. I just never saw an emulsion tube move so easily before, but as it's up even with the other ones I'm assuming it went back in the notch. I set the mixture with a colortune, and it was running perfect until yesterday afternoon. Something went caflewy.

The other thing is the plugs keep coming out a nice medium brown. If the carbs were causing the problem wouldn't you expect it show on the plugs? I keep coming back around to a vacuum leak, as it does kind of act like it did the last time I forgot to put the blind plugs back on after a synch .

[DGXSER]

Doug, you gave me a thought here. Have you tried putting the vacuum cap form say #1 on #3 and seeign if the problem moves? Perhaps you got a small hole in #3 cap or something?

[Crazcnuk]

Yes, I would expect it to show on the plugs, but an idle issue may take an hour of idling to do that!

I had a similar issue, yesterday, too. Maybe it was just a wierd day!

My bike was running great. Friday, I took the tank off so Derwat could clear coat it for me. Later that night, when I put it back on to go home, I (didn't know at the moment) kinked the fuel lines putting the tank on in the dark.

I got about a block, and the bike died. After some fiddling I put the petcocks on 'prime' and drove home.

Next morning was the Show n Shine, so I left them on prime.

It sat there at the show all morning, no leaks.

At the first stop on the poker run, It leaked about a 12" circle of gas, and did not want to start. For the nest 3 legs the bike ran rich enough to see at the tailpipes (sticking float?)

As we left for the last leg home, the bike all of a sudden started bucking, like it was running out of fuel (left side only). I fiddled as I rode and ended up putting the petcock (left) back on 'run'. The bike settled down, so I put the right side on run as well. It has run fine ever since....

[dbeardslee]

Don - Had the same thought and some extra blind plugs, so I put four different ones on when I did the synch. Besides, it was doing it with the vacuum gauges connected and the blind plugs on the bench. That was good noodling, though.

Craz - I was hoping the seafoam was going to work it's magic on these carbs last night, but alas I think Betsy wants some hands-on attention - women! I think tomorrow I'm going to pull the carbs again and take the boots off and see if there's anything that looks like it might be leaking air. The problem gets worse as the motor heats up, so maybe something is expanding around the boots, or the rubbers getting softer at that temp, or who knows what. One way to find out.

[fredintoon]

- - - I installed pod filters last year. Has anyone had a problem with carb boots leaking after installation of pods? Without the support from the airbox, all the weight is supported by the carb boots, so I just thought I would ask.

Hi Doug,
there's warnings about that on this site someplace. Luckily for me I read 'em before I dumped the airbox in favour of Unipods. Pods work like magic, ever since I put 'em on I have not needed to remove & clean the carbs at all.
Nor do the carbs flex on the carb boots because I built a sturdy metal bracket to hold their back ends up.

[dbeardslee]

Fred - The more I think about it, the more I think a vacuum leak is the culpret. It kind of threw me, as I had just been in the carbs, so naturally that was the first place I looked. The carb hangers have been holding up the pods for about a year now, and with the pressure you have to put on the boots to reinstall the carbs it makes perfect sense that it could develop a vacuum leak immediately after installation.

For maybe the past three months or so she's been farting through the carbs intermittently. I kept looking at carbs, synch and timing as the culprets, but now I'm thinking it was probably vacuum and rough roads making the carbs bounce around.

Do you have any pictures of your bracket?

[DGXSER]

Doug, Eric had one on his bike, did you see that one? Went to two of the screws in the brace across the four carbs and then up to I think where the air box used to bolt up to the frame IIRC.

[pete_s]

I would do a quick compression test, and or check valve clearance and see if #3 is different.

Make sure the throttle and slides are open when you test and write the results down for future reference.