1979 Intruder - Post Season Diagnostics

[mswyka]

It was an odd year for snow here in NY.  We got in some good riding, but only late in the season.  Not enough riding to get all of the sleds out for exercise.  We did manage to pull out the 79 Intruder for one run.  However, it proved unreliable and ended up going back in the barn after about 10 minutes.

The sled started well, idled well and took off well.  After a friend gave it a few laps I took it for a run and pulled the throttle wide open and she tore down the lake.  After what was probably only 30 seconds she started to slow and continued to slow until I thought it would die and started limping back to the barn.  It made it and off the lake and out of the deep snow she was a little more responsive - but still not right.

A week or two later I pulled the sled out of the barn to bring it home and of course could not resist pulling out onto the lake only this time it really did not want to pull any rpms so I limped back again and loaded it up onto the trailer.

Back at home today I started post-season diagnostics with a compression test.  Cold she measured 150 both sides.  Then I warmed it up a bit and measured again and got 135 both sides.  My sense is that neither of those numbers would account for the performance I witnessed and on that basis I want to assume that pistons and rings are not a problem and I should be looking somewhere else.

Appreciate thoughts on next steps.

[Interceptor398]

My first guess is it's starving for fuel if the compression is OK.

[gixxer6]

I agree, sounds like a possible fuel issue.  How do the plugs look? 

[Interceptor398]

After thinking about it a plugged exhaust might act like that?

[mswyka]

Thank you both for the suggestions.

I can see both conditions potentially causing or contributing to this issue.  I will need to get it into the shop and start checking it out piece by piece. 

Thinking about fuel restriction, I remember another Intruder that we were working on a few years back that was having a similar difficult running properly.  When we pulled the clunk out of the tank it was full of crud.  Once we swapped in a clean tank the problem went away.

I am curious if there is a standard technique for gauging flow restriction in an exhaust? 

[gixxer6]

I’m not sure if it’s a standard technique, but I put my shop vac on the inlet of the pipe and feel the suction on the tailpipe.  I also physically shake the pipe while doing this to see if there’s something floating around in it. 

[mswyka]

I’m not sure if it’s a standard technique, but I put my shop vac on the inlet of the pipe and feel the suction on the tailpipe.  I also physically shake the pipe while doing this to see if there’s something floating around in it.

Makes sense.  At least I've got some things to keep me busy in the near future.  The sad part is that without snow I won't really know if I have solved the problem until next season.

[gixxer6]

Unless you are able to find the “smoking gun”. 

[Interceptor398]

Snow is not required to have fun on a sled.

[mswyka]

I have begun to make some progress.

Pulled the clunk from the tank - all is clear

Checked layout of fuel line for kinks - all smooth curves with no pinch points

Checked fuel filter - filter had almost no debris

Tested fuel pressure in an effort to determine if fuel pump is delivering enough fuel.  Pump is putting out 5 psi at idle.

Noted that enrichners were fully wet on both carbs.  Not sure that this should have been wet if seated properly. - more to check here.

Checked fuel needles/seats to make sure that I didn't somehow install needles that were too small.  Fuel needles are 1.5 - so not the stock 1.2, but should not be restricting flow.

Started to think about the dreaded "O" ring.  Both "O" rings looked to be intact.

Not sure at the moment where to go next.

[Interceptor398]

Were there air bubbles in the enricher lines while running?

[mswyka]

Were there air bubbles in the enricher lines while running?

Good thought.  I neglected to check for bubbles in the lines before pulling the carbs.  I will need to check this when the carbs go back on.

[gixxer6]

Verify that the enricheners are adjusted properly, and check the rubber on the bottom of the plungers, I have seen them crack over time. 

[mswyka]

Verify that the enricheners are adjusted properly, and check the rubber on the bottom of the plungers, I have seen them crack over time.

Good thought.  I had not thought about cracking.

[Ameritude]

check your coil, similar issues have come up for me and a new coil fixed them. usually its with heat it starts to crap out with the coil, but you never know.