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Old 01-06-2009, 09:25 AM   #1
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Default Air Leak from Pull Start?

I got a brand new Hyper 7 with macstar .28 last week. It ran great right out of the box. I followed the break-in procedure to a tee last Friday and got 12 tanks out of it.

As I was going for one last start, the rope pulled clean out of the pull start mechanism.

Two days later I went to the track with a new starter box and couldn't get the engine to fire no matter what. After richening the needles considerably, we got the engine to run, but erratically. It wouldn't transition well and was cutting out. It also needed to be slobbering rich to run at all, with raw fuel coming out the exhaust.

I've done some research and this behavior sounds very consistent with an air leak. We changed the plug numerous times and used multiple ignitors, so that wasn't the problem. I hadn't touched the mid-needle but had leaned the main and low needles very slightly (about 1/4 turn) and the engine was still running rich after the first day.

Does the fact that the pullstart rope is gone cause an air leak from the pullstart mechanism? I am planning on putting in a regular backplate shortly, but would also like to send the engine in to Ofna for warranty service given that it's only a few days old.

Thanks in advance,
Dominic
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Old 01-06-2009, 10:29 AM   #2
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Dominic,

You bet a back plate can leak and cause irratic running (lean). I rebuilt a Traxxas Pro .15 and ended up replacing the back plate because the start shaft through the back plate was very worn and caused an air leak. But this was an old engine.

There are occasionally bad engines out of the box, but that is the exception, not the rule. If the back plate is leaking the inside of the recoil and the one-way bearing will be really wet.
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Old 01-06-2009, 10:45 AM   #3
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Thanks Chuck - the one way bearing was pretty wet when I looked at it last night. I really hope the new backplate will solve the problem. Pullstarts suck!!

Dominic
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Old 01-06-2009, 10:46 AM   #4
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ALL pull starts have air leaks within a few tanks...just how bad is it going to be.
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Old 01-06-2009, 03:43 PM   #5
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It seemed like a bad idea from the beginning, I just hope that's the problem - the car has less than a dozen tanks through it.

EDIT- now that I think about it, I might have caused a leak by taking the pullstart off to fix it, and then replacing it. Problems like this really challenge me but they're very satisfying to fix once the engine gets running well again.
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Old 01-13-2009, 10:13 AM   #6
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Installed new backplate and laid some RTV gasket sealer in the joint. Problem solved. Engine runs very well now. Thanks to all.
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