Hi there. I have a 1985 Harley Davidson Iron Head Sportster 1000 that I am trying to get running good again. I am a Harley technician but I'm more familiar with the late model Harley's. I have tested and changed a few things on it. I installed a late model CV carburetor (not to solve the issue, but to make it run better). Seems to start great when cold. Takes about 5 minutes to warm up. I take it down the road and runs great. I return to my shop and it will hold an idle just fine. I then shut the bike off and let sit for a few minutes... then try to start it back up. It starts with a little help from accelerator pump, but will not hold and idle unless it is run again for a few minutes down the road or the choke is out. The points gap it good. New plugs and wires. Fuel tank and screen are clean. The jets are 175/45 with a perfectly clean carburetor. Intake seals and inlet boot do not leak. The compression is around 90PSI. I feel is a little low but im hearing this is normal. I want to get this thing going but I'm lost with it not holding and idle after it is restarted hot from a 5 minute rest... Please help? I feel like I'm missing something...

 

Will it hold idle from a hot start with choke pulled out a bit? If so, that indicates it needs more fuel and you'll need to upsize the idle jet. 90 compression seems low, maybe do a leak down test. Also check for air leaks on the intake side.

 

Did you do the compression test when both the engine was fully warmed up [as in a 30+ minute ride out of city traffic] and the throttle was wide open while cranking? If you ensure both of these you may get higher readings. It is also possible that pushrods in both cylinders are too tight resulting in low compression readings ...

Ironhead Push Rod Adjustment
http://xlforum.net/vbportal/forums/s...ad.php?t=44143

It is possible that the test you are using is not fair, so to speak. Start up, 5 minutes to warm up [thus fouling the plugs if it is idling with the choke on], short ride down the road [not long enough to clean the plugs], let it idle in the shop [not able to clean the plugs], start with acc pump [more plug fowling], ... through all this it never gets fully warmed up.

What I would do is start it, warm it up using choke for no more than 30 to 60 seconds, ride off keeping it running with the throttle, get out of city traffic and ride for at least 30 minutes.

Heck, ride longer like 45 minutes plus. Get it really fully warmed up. Before leaving the shop for this ride have your compression gauge, spark plug wrench etc ready. Do the compression test immediately upon arrival back at the shop.

I do this about as often as I do oil changes. I write down the numbers. My bike has had compression 150/150 for in excess of 60,000 miles. If a compression test is ever low I know absolutely that it is a pushrod gone tight.

Cylinder Compression And Leakage Tests For Your Ironhead
http://xlforum.net/vbportal/forums/s...ad.php?t=48311

 

If the choke is needed to roll, after warmed up, then either the pilot jet, air/dle mixture setting, or an intake leak.
Scott

 

if you did not take the carb completely apart before installing you could have a bad boot or its not seated correctly