Bad Idol

[bkmarsha]

heres the story

rebuilt engine, had air leak at carb holder, got fixed not 100% but better, took two hour ride (to get back to school), lost left cylinder half way thorough (believed to be because by air leak), ordered new holders from JBM, instaled carb holders, checked timing, also replaced atu springs on rebuild

problems

the bike runs porly at idle and trys to die and back fire out of left carb. when reved it runs much bettter with little or no problems but wants idle to hang up at 3000-3500 if above 1700 when clutch is pulled in. if you get the engine speed below 1500 it will idle at a normal speed

i am wondering what is causing the problem

i have thought that i may still have a minor air leak, maybe a blockage or improper adjustment of carbs (good carb cleaning was my next guess without any other sugestions), or potential damage from running the engine on one cylinder shortly after a rebuild

hopefully someone will have some idea and maybe point me in the right direction

 

[inxs]

- are you still having problems with your advance mechanism

- throttle cable damaged or dry? routing problem?

- pilot jet, idle screw o-ring, slide catching, sync?

 

[Sundie]

you didn't mention year - but if you're running points and mechanical advance, check your springs on the advance mechanism.

 

[weekendrider]

bkmarsha did you use Mikes springs? If so several have reported having to cut them shorter. Cut the hook off and use the first coil to make a new hook.

If you check the springs and they are returning I would revisit the places an air leak could occur boots, and throttle shaft seals in particuliar.

 

[bkmarsha]

its a 78 with the pamco ignition so no points

the springs are from mikes how dod i check to see if they are returning

throttle cable dry? does it need oiled

how do i check the throttle shaft seals

 

[inxs]

its a 78 with the pamco ignition so no points

the springs are from mikes how dod i check to see if they are returning

- manually with your finger-pull them out and let them go-should snap back
- can check with engine running too using a strobe or timing light

throttle cable dry? does it need oiled

- yes unless theyve got teflon liners

how do i check the throttle shaft seals

- engine running, spray starting fluid on the throttle shaft entry and exit points, also separately do the manifold rubbers...any noticeable change in idle speed or quality will indicate leaks

 

[bkmarsha]

i have a fairly new throttle cable from mikes (ordered and instaled end of last year) how and where do i need to oil it

i have used the starter fluid method before i just have trouble being precise with the spray when i suspected i had a boot leak it may have been the throttle shaft seal the whole time

is that a repair or a replacement

 

[retiredgentleman]

bkmarsha;
With a hanging idle like that, you need to adjust the carbs. You need to do a "dead cylinder" adjustment of the pilot (mixture screws). However, in order to do that the carb butterflys must be able to go completely closed. I would remove the carbs and confirm that the butterflys are closing completely.

To do the "dead cylinder method" you must adjust the "idle mixture screw" (pilot screw) as well as the "idle speed screw". You should be able to adjust the engine speed down to around 200 or 300 rpm on 1 cylinder firing. If you can't do that, then you're not doing it right,or you have air leaks etc. You have to adjust both screws to achieve this. As you adjust the pilot screw, keep lowering the idle speed screw to get the rpm down. Adjust the pilot screw for the "sweet spot", meaning the smoothest highest idle.

The important thing to realize, is that the throttle butterfly must be almost completely shut, in order that the pilot screw can be adjusted. This is because the butterfly must be covering up the 3 by-pass holes in the carb throat. If the butterfly is open even slightly, the mixture coming through the 3 by-pass holes over-rides the pilot screw, and you are unable to adjust it.

If someone has had the butterflys removed from the carbs, they may not have re-installed them correctly. The butterflys need to be self-alined. This is done by leaving the butterfly screws loose, while allowing the shaft and butterfly to fully seat against the side of the carbs.............the screws are then tightened (use thread locker on the screws).

 

[bkmarsha]

today i took apart both carb cleaned all parts as good as i could then reasembled

i made sure that the three holes are covered when valve is closed

now the backfire has moved to the other side (now on right) and the idle seems to be better or fixed

going out on a ride tonight and give updates later tonight

 

[bkmarsha]

so scratch the ride not going to happen the back firing is sever and will not run without the choke on

im starting to think that i may need to take it to someone who knows what they are doing

 

[retiredgentleman]

You say you have cleaned the carbs, but have you looked closely at the pilot jet under a magnifying glass to confirm that the very small orifice is completely clear? Once they are checked clear, you still need to adjust the pilot screws (mixture screws) using the "dead cylinder method". Be sure to ground the high voltage (can use a dummy plug)on the dead cylinder to prevent damage to the ignition coil and/or pamco.

 

[bkmarsha]

i visually checked to see that all the jets were clear (held up to light and could see though them)

i then set the mixture screws the generic 3/4 of a turn out

i can not get it to run well enough to even try the dead cylinder method it has a severe backfire on the right side when the choke is not on

 

[inxs]

- needing choke suggests its running too lean...recheck your pilot circuits and then do it again, when you think theyre clean-reclean them...use compressed air too, and be merciless...make sure your gas and tank are clean and use inline fuel filters
- other things to check or recheck
- vacuum leaks
- air filter
- spark plug gaps too tight or plugs cracked
- timing retarded
- worn cam lobes
- sticky or burnt valve
- valve not set right
- .........???

 

[weekendrider]

Are the o-rings on the mixture screws OK?

 

[TeeCat]

Hey RG -

I'm not sure if BK has one or two throttle cables on his bike, but mine has two. Thinking about the role of the pilot and idle speed screws in the dead cylinder method, it seems to me that in order for independently cabled/throttled carbs to be physically synched, both idle speed screws would have to be identically set so that the butterflies operate in as close to unison as possible. The only other adjustment then, it seems, would be the pilot screws. That said, if one has a bike with two cables, can one synch the idle speed screws/butterflies, and then "fine tune" the pilots? That seems to make sense to me.

In hindsight, I can see where the method you describe would work a charm with one- cable bikes, but on a two-ie, those dadgum idle speed screws must be identically set, so the only other variable would seem to be the pilots.

Hope this question makes sense.

 

[xsjohn]

I shouldn't get in this but...........set the sync as best you can......may have to revisit later..........cruise along easy say at 40 or so at low throttle with the engine "fully" warmed ........stop after 3-4 miles and check the plugs....setting each mix screw independently....should be almost no soot on the ring checking with the end of your finger........no soot it is probably lean and very noticable soot would be rich....just a "very" faint trace of soot is what you are looking....and look at the ground strap.......good tuning and the black will be about 1/3 the way up the side of the ground strap and listen to the engine as you go to see how it is operating.......soon you will just know how to set them and which cylinder to mess with.......at 40 or so on easy throttle you are almost all on the pilots...and mix screws......if not all..........

xsjohn

 

[TeeCat]

Hi, John...

....setting each mix screw independently....

See, this makes more sense to me now. I had always thought that the idle speed and the pilots needed to be identical on both sides, but you and RG - and griz, I think - seem to agree that the pilots might not have to be identical. Mine are both at 3/4 and I'll have to diddle with them. I jumped in here because BK's issue is somewhat similar to mine.

 

[xsjohn]

Would guess that no 2 carbs are indentical and the right requires a bit more fuel because of it's elevated temperature......and connecting the barbs like pete says with 3/16 ID tubing when you are done helps balance things better.....re adjust idol with the tubing....................

I don't see how people tune these without actually riding it.........

xsjohn

 

[TeeCat]

Meh.. .see, I don't have barbs, though. Not sure if BK does or not.

Say, for BK's info too... how far out can you go on pilot screws for early bikes before they're not metering at all any more?

 

[xsjohn]

If you are at 3 turns or near I would try the next size pilot...not really totally sure about the early bikes...maybe someone that has the early ones has tried this....generally 1/4 turn per pilot size from what I have found ........but as you go up on the pilot the turns get more sensitive...and there is a limit I would suppose.........bound to be able to drill and mount barbs using superglue.........I fixed a loose one that way........

xsjohn