off idle - too rich or too lean?

[psycoreefer]

Hey all, I've been going round and round with my carbs. I just installed new needle jets and that seems to have cleared up all the upper RPM problems I was having but now I've got issues just off idle. Seems strange that new needle jets would effect my mixture that low down because before it was fine.

The bike idles fine and has good compression but if I crack the throttle 1/8th with no load the bike will choke and die after a second or two. If I continue past 1/8th slowly the revs will pick up right to red line. If I suddenly crank it all the way open, dies right away.

Under load riding around town I've got no power at take off untill I get up to around 2.5k then it kicks in and runs strong. Once above that point and ridding around I can cruse with little throttle or crank it all the way open and it responds as I'd expect.

I'm thinking this is mainly effected by the three holes that are part of the idle circuit but not adjustable by the idle screw. Anyone wana back me up on that?

Any way for me to figure out if I'm to rich or lean at that 1/8th opening? It won't run long enough to color the plugs so thats out. I've tried adjusting the float hight up and down and that didn't seem to have any noticeable effect. I don't have the money now for a color tune so thats out also unless someone in west MI wants to let me borrow theirs.

[boyat68]

psycoreefer:

It seems that you have to do a new synch first, then reset your idle mixture screws. Every time that I took my carbs off and diddle with the float levels I had to re-synch using my synch gauges, then touch up the idle mixture screws. Until I did this the bike would start and creep up the RPM range until the bike was screaming at 6000. The minute that I synchronized , then the RPMs would fall, I would then reset the idle to 1100, re synch, reset the idle etc., and dial the bike in. I started this with the idle mixture screws set at 1-1/4 turns out. I would then look at the color of each plug and try to get the plugs looking good by moving the idle mixture screw 1/4 turn.

[oseaghdha]

Something wrong in the idle circuit.
It has to cover until the mains start up.
Check the float levels, check the idle jets.
Where are your screws set?
If you have aftermarket floats, you should check the fuel level externally. Set it at the split line of the bowl/carb body.

[psycoreefer]

Idle jets are new and clean. Idle passages are clean. This problem only started once I replaced the needle jets with new stock needle jets. Floats are currently set at 26mm, I've tried everything between 24 and 27 in .5mm increments and no changes. Thanks for backing up the idle circuit idea, but how do you adjust the "other" idle circuit outlets. Only by float level or idle air/fuel jets right. I can't believe I need something other then stock jets given my setup. Could timing, ignition or valve, effect only the lower RPM's but not the upper?

The floats are the ones from MikesXS, someone here did a test and reported that the plastic floats set the level the same as the old brass ones. I could find the thread if anyone's interested. I guess I'll pick up some grease fittings to drill out so I can check the level if the synch doesn't fix things.

My idle doesn't creep up, it idles nice and even but won't take part throttle.
I haven't synched the carbs after the new needle jets so I guess I'll give that a try tomorrow.

[oseaghdha]

Ideas

Start at the beginning:
You replaced the "needle jets". Do you mean the main jets?
Are they 137.5s?
Why did you replace them?
What were the old ones?

Do you have the brass washers in place( under the mains)?

Did you replace or clean the emulsion tubes?

The passage to the idle circuit comes thru the main well.

Does it work better with the 'choke'?

Where are your idle screws set? 1 turn, 2 turns, 3 turns?

How do the spark plugs look?

All the vacuum caps are good?

Spray the boots for leaks?

Dunno, process of elimination.

[psycoreefer]

needle jets = emulsion tubes, one had the ring broken off the top and another had visible scratches down the inside of it. Replaced with new old stock 266 - x2 jets, same as what was removed.

Idle jets are also stock size, replace because 3 of the four had the screw head striped out so I couldn't get them out for cleaning. Removed with an easy-out and replaced with new of the same size, can't remember now what that is but it was stock for my year.

Mains are 137.5 - also stock size. I've also got 140's but they aren't in the carbs right now, the 137.5's seem to run better. Yeah I've got the brass washers under them.

Idle screws are between 2 and 3 turns out, idles nice and smooth there but plugs are maybe a touch on the dark side but no where near "fouled". Just a light gray around the tips instead of nice tan.

It runs better with choke but only because with the choke on it idles above 2k so Its already above the problem range and into the OK range of running.

Spark plugs look good but I can't run it at the problem speed long enough to color the plugs because it dies first. I wish I could get it to run there a little longer so I could get an idea of which way I'm off.

Vacuum caps are good, checked both visually and by raising the slide and putting my finger over the crescent shaped port on the front of the carb - all dropped very slowly and at the same rate as the others.

Checked for leaks with both starting fluid spray and with an unlit propane torch. Didn't find any.


I've tried everything I can think of and I've gotten nowhere on this. At this point I'd be taking the carbs off and making random changes because any change I think could work I've tried with no improvement. Any other suggestions?

[randy]

I think you have a vacuum leak.

[wa407mpp]

pilot jet problem

Check the passages to your pilot jets, you are not getting a good transfer from idle to open throttle, which is the pilot jets job, so when you open the throttle to quickly it leans out with too much air, then the main jet eventually makes up the difference and then it is ok. Those scratches were wear marks and were probably letting enough extra fuel bleed through to make up for the pilot jet problems, so they went unnoticed before the new jets were installed.

[psycoreefer]

Randy - I'll check again for vacuum leaks, is there any other, better, way then using starting fluid or an unlit torch?

wa - I like your thinking on why the problem showed up now. Do you have any suggestions on how to check that the pilot circuits are clean and clear. I've put at least 3 cans of carb cleaner through each carb and I get a good solid blast of spray out of all the pilot circuit holes when I spray into the pilot air jet. Is there another method?

On the task list for this week so far:
Re-synch carbs again = free
Re-check for vacuum leaks = free
if those fail
More carb cleaner in the idle ciruit = $$
Get supplies to visually check fuel level = $$

Thanks again and keep the suggestions coming!!!

[boyat68]

psycoreefer:

Is it possible that you have a broken off Pilot Screw blocking one of your passages? or something in that hole. It is very tiny and if it is not clear it will screw things up.

[psycoreefer]

I've got new pilot screws in it and I get carb cleaner spraying out the holes (including the one the pilot screw controls) when I spray it into the idle air jet so I know there isn't a screw tip blocking off the port completely. Now I think its clean as I've completely disasembled and cleaned the carbs several times but there isn't really any way to know for sure. If nothing else works I'll guess I'll try cleaning them again.

On that note I read a tip on another site that suggested complete disassembly and then boiling the carbs in water for 5 - 10 minutes to help clean internal passage ways. According to them this doesn't require the removal of the "throttle shaft seals" that get ruined in carb cleaner dips. The claim is that its safe because all the parts are designed to withstand engine temperatures near 200 anyways and the results are close to that of ultrasonic cleaning. Anyone know if its safe for our carbs?

[egsols]

You say you replaced the emulsion tubes and needles?

Are the replacement emulsion tubes exactly the same. The 79s had more holes that the 80s and I also believe the ones for 2 and 3 were slightly different than the ones for 1 and 2.

If you replaced the needles are they also the same length as the old ones? I recall someone ordering a set and upon close inspection they were a different length than stock and the tip was also slightly different.

I have doubts that anything in your carbs is clogged as you say the carb cleaner shoots through but additionally it ran good before you did the change.

[boyat68]

psycoreefer:

If you do the float fuel height check that Ken pioneered, then you will know for sure that your Pilots are getting enough fuel as your carbs receives the pilot fuel directly from the bowl and the pilot jets are above the main jets so if you run low in one bowl ala the other bowls then that carb may be starving when going from idle to mains. This should not really happen, but you never know.
Just a WAG

[psycoreefer]

egsols -
I replaced the emulsion tubes, they were Identical to the ones from cylinders 1 and 4 marked 266 - X2. I put the same tubes in all four carbs despite coming from the factory with a leaner tube in 2 and 3. I suppose that could be the problem but I can't see any reason why cylinder #2 would need a different mixture then cylinder #1 other then emissions BS. I did not replace the needles as I couldn't afford both new needles and new emulsion tubes and I could see the tubes were damaged while the needle look fine. It has stock needles 5GZ6. I do have new after market needles but I'm not using them due to them being longer and a different taper then the stock ones as you mentioned.

Also it wasn't running right before, it sucked in the mid-range and high RPMs and was very rich on one cylinder, thats why I got the new jets. Its just that before it ran real well down low below 3k now thats where all the problems are. I like the idea mentioned earlier that the old leaky jets were covering up the low range issue while causing the upper rpm issues.

Boyat-
I'll definitely check the fuel level if the free checks don't turn anything up. My pilots don't pull directly from the bowls, they pull through the mains. The pilot towers have a screw cap over the end of them and there is a passage between the main tower and the pilot tower. I checked the parts fiche and it shows the cap screw so I think its correct for my year.
Its my birthday so money is tight this month, I hate that insurance and tags all need to be renewed on your birthday. So I just don't want to spend the cash on clear tubing, and fittings so that I can attach lines to the carbs unless i really don't have any other choice.

[randy]

psycoreefer;

Something in your signature caught my eye. You have a MAC 4-into-2 with stock jets (137.5's)?. That may be your mid-range issue. I run 140 main jets and the floats are about 1mm richer.