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Sanity Check Please - Cold Start Issues

  • Thread starter Thread starter nater
  • Start date Start date
N

nater

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I need someone to tell me this makes sense before I start down the wrong path. Some background...spent the winter properly dipping and rebuilding the carbs with new orings and original stock jets, bench sync'd then idle sync'd by ear. All new rubber on the intake, stock airbox and exhaust. I recently re-adjusted the valves, new petcock and fresh gas.

When I go to start the bike, 3/4 cylinders kick in and the bike will barely idle with full choke. After 2 mins or so, like a switch the last cylinder will kick in and the rpms take off. after that, the bike will idle and run great until the next time i try to start it.

I know tough starting can be valves but i just adjusted them...do i need to again or am i missing something?
 
tkent02 said:
Try vacuum synching the carburetors and doing the other adjustments..
Click to expand...

Agreed I need to vacuum sync but it idles like a rock once that last cylinder kicks in...really think that could be the difference? I guess i'll have to start saving my pennies.
 
Look at the choke circuit for the carb that fires up last, it may be clogged somewhere. Easiest to check is the fuel supply well in the float bowl itself, there's a small orifice where fuel comes in from the main part of the float bowl that clogs often.
 
It certainly won't hurt to check the valves again. I have had that happen a couple of times, where something had stuck in the valve seat because the bike had sat for so long. Doing an adjustment before running the bike to clean the seats only adjusted the clearances to the "crud", not the seats. Now that your bike has been running for a bit, try checking your clearances again.

.
 
My 650 has the same problem!
I have yet to even take a crack at it, I barely ride it.

I was thinking choke problem, or valves...based on my bikes history
 
I had a bad spark plug cap (#1) creating the same symptoms on my 650 recently. Replaced the cap and presto-chango. No problems with startup.

Of course, it wouldn't hurt checking everything else mentioned so far as well, but at least the spark plug cap is an oil-free check.
 
tkent02 said:
Look at the choke circuit for the carb that fires up last, it may be clogged somewhere. Easiest to check is the fuel supply well in the float bowl itself, there's a small orifice where fuel comes in from the main part of the float bowl that clogs often.
Click to expand...
Yes, and probably other carbs have some blocked choke citcuits too....

"When I go to start the bike, 3/4 cylinders kick in and the bike will barely idle with full choke. "

Thing should take off with full choke-even on just two carbs with working choke circuits. Little hole in bottom of all bowls should be poked and blown out.
 
tom203 said:
Yes, and probably other carbs have some blocked choke citcuits too....

"When I go to start the bike, 3/4 cylinders kick in and the bike will barely idle with full choke. "

Thing should take off with full choke-even on just two carbs with working choke circuits. Little hole in bottom of all bowls should be poked and blown out.
Click to expand...

Hmmm...ok good to know, i guess that will be my first thing to check then. That would be great if it was something so straightforward. Honestly the choke circuit never came to mind, but thats where you guys come in. Choke circuit and double check the valves again.

BigD: recently changed the plug caps also but i'll double check that all my connections are solid.
 
Ok, its been a few weeks but just to update. I removed the carbs again and cleaned the entire choke system - removed plungers and float bowls, sprayed them all out and ensured that carb spray was spraying clear through the correct passages (This was after a proper dip previously). Also, I bought a Carbtune Pro and sync'd the carbs once all cylinders were running. My numbers are now (from left to right) 21, 20, 20, 22.5, which is as close as im gonna get lol.

Annnndddd...no dice. Exact same problem as before. Tom was right, it was only running on 2 cylinders to start. The final cylinder kicked in a few mins after the third one, I just hadn't let it idle that long previously.

Next step is check valve clearances again, but they were not that far off to begin with, so im not holding my breath!
 
No need to do that. When its cold start it then immediately feel the pipes. The cylinders that are firing will be warm. Don't let it idle too long before feeling the pipes obviously.
 
Cylinders 2 and 3 fire like they should, i.e. pipes HOT lol. 1 hiccups and pops on and off with some throttle (pipe pretty darn hot), and 4 will come alive also but is harder to keep going (pipe warm). I checked valve clearances again this morning and everything is within spec. Also pulled the plug caps, cut back a bit of wire on each and reinstalled. Finally pulled all the plugs to check their color and gap...cylinder 4 is black but the rest look alright.

I'm starting to run out of options, which I think is a good thing...do the carbs have to come back off? :( I am so close to having this thing back on the road, just cannot seem to find the source of this last issue. Thanks again for all the help.
 
I would check the ignition system first since it is both 1 and 4. How is the condition of the coil and spark plugs on those cylinders?
 
I agree with electrical since it's 1 & 4 that are not firing (they are controlled by the same coil). What does the spark look like on those two cylinders compared to the other two that are firing properly?
 
Sure makes you suspicious of ignitor circuit that fires 1 and 4 at cold start. Also, is bike typically on kickstand during start ?- even on "prime" spot maybe #4 doesn't get enough fuel initially.... BUT. the black #4 plug says otherwise.
 
razor02097 said:
I would check the ignition system first since it is both 1 and 4. How is the condition of the coil and spark plugs on those cylinders?
Click to expand...

I feel like an idiot not checking this before, but you're right this makes the most sense to check. The resistances of both coils check out, and to double check this i swapped the 1/4 coil, wires, and igniter pin onto the 2/3 cylinders and it idled on those two cylinders just the same. Also, I've got a solid 12.2v to each coil (12.5 at the battery), so coils, wires and plug caps should be ok.

Tom - I'll do the igniter test tomorrow, but based on everything so far i think it makes a lot of sense.

I'll have an update shortly!
 
I had a nighthawk that did the same thing when I got it. A good carb cleaning fixed the issue. Maybe you should revisit the carbs.
 
Well...igniter looks like it's working just as it should and i've got nice blue spark on all four plugs when I jump the corresponding igniter leads. Also, I have 157 Ohms on both the pickups, so looks like my ignition system is working as it should. Was good to go through, but sucks not finding the culprit.

It's really interesting that if i stay off the throttle and just idle, even below a few krpm, cylinders 1 and 4 NEVER catch. Oh well, back to the carbs...
 
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