Box Stock

Help getting a clone to start

J

jacobsdad

Member
Last weekend my daughters engine gave up. I have a box stock clone here that has maybe 20 laps on it, I decided to put that on her kart to get by this weekend. It had a problem with the cylinder head so I traded heads with another engine. I opened the case and cleaned everything up inside, put it back together and it will not start. Every 10th or 20th pull off the rope it will backfire and spit fire out of the exhaust. What am I missing?
I liked the timing marks up on the cam and crank gear. I thought maybe I missed the marks so I pulled it apart and re lined the timing marks, twice. Valve lash us good. Coil gap is at.035. I tried it wider and tried it smaller. It is getting good spark. I pulled the flywheel and checked, the key is in right And is not sheered off. I even tried a different flywheel. I tried a different carb. I even tried ether into the carb and still no start.
I can not think of anything I did wrong or am missing!
when it does backfire out the exhaust it is not a Big Bang, it is a little pop.
just to make sure, both intake and exhaust push rods and lifters are the same length right? The lash cap goes on the exhaust valve correct?
 
Sounds like valves too tight like he mentioned above. Lash cap on exhaust correct. What flywheel? Arc says its gotta be .035 or more and suggests more.

Did you degree the cam and check the timing? Sometimes you can think the flywheel is correct and you actually turned it the opposite way
 
Let's look at the basics; if the engine has compression, and it's getting spark, at the right time, and fuel, again, at the right time (valves), it's got run, period. If those things are perfect, it run its best, but if they're not exactly and exactly on her out and perfect, it'll still run, just not as good.
We always check the spark plug first, is it sparking. 2nd, is it getting fuel? Both good? Is it getting those 2 things at the right time? Check.
 
That is what does not make sense.
valve lash is correct, but I will check it again just to make sure. The symptoms say timing is off, but I used the same flywheel key it had in it before, and it ran before.
I’m going to take it apart and check everything again.
 
Valves not stuck ?
Roll it up to tdc and see where the magnets are in relation too the coil .
One good back fire is all it takes to shear the key .
 
Got spark and fuel...back fires through intake or exhaust its timing. Just a dumb question is the gap on the spark plug closed up..?
 
Just to be safe open the gap up on the lash and try it. Some guys say you can preload it I tried that with the dial indicator and they must be better than me I couldn't ever get it to start. I think someone mentioned a starter box if you are doing that and I don't have one so that maybe why.
 
I’m back in the shop now finally. The spark plug is an auto lite ar3910x so it doesn’t have a strap to gap. It is getting a good hot white spark.
it has fuel, air, spark so all that is left is compression and timing. I checked the flywheel key and it is good. It is a standard key, not an advance key. I checked the timing marks on the cam and crank again, they are lined up.
 
Here is a picture. I tried a video but can’t figure out how to post it. This is at top dead center, this is where the magnet is riding. Valve lash changed to .02 on both still nothing.
it has only backfired a couple of times, and not a bang just a little bloop with fire out the exhaust. I’m going to pull the head and make sure the valves are seating tight and report back.
 

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That picture looks wromg to me . Read the blue plate post jpr57 explains it .
You physically removed the flywheel and checked ?
 
flattop1 said:
That picture looks wromg to me . Read the blue plate post jpr57 explains it .
You physically removed the flywheel and checked ?
Click to expand...
I have one with the degree wheel on it in the garage now. Looking at his and mine they are within 3/4 degrees. after looking I agree his timing appears to be ok.
 
Yea maybe so . I just measured this one from the line to coil is 1 5/8ths inch .
Actually jacob did me a favor the other one was sitting with no spark plug in it , i just went through it last winter not sure how long its been out .
 

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flattop1 said:
Yea maybe so . I just measured this one from the line to coil is 1 5/8ths inch .
Actually jacob did me a favor the other one was sitting with no spark plug in it , i just went through it last winter not sure how long its been out .
Click to expand...
What do you believe you have for timing?
 
I got it. It was the exhaust valve not seating tight!
I am basically combining old parts to make something run so she can race Friday night, just to get by until I can find a new engine. The exhaust valve seat needs reground. I used a different head and it started right up and runs good.
I am running whatever timing the ARC flywheel is, I think 32 degrees.
Also I am running the coil gap at .035, where should I set it? I can’t remember butI was thinking I was always closer to .050.
 
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