787 turns over but will not start

[gcha1727]

Any input is appreciated..

I have a rebuilt 787 motor that hasnt ran. It turns strong but is not close to firing. I had to buy used carbs from someone for this motor but not sure if there is an internal problem with them.

So far I have done the following;

Checked compression..just under 150 psi in each cylinder
Verified spark for each cylinder
pulled carbs out/apart and cleaned..passageways clear..new fuel filters
If I push on accelaerator pump I see fuel spraying into each carb
Pulled rv cover and verified rv in right spot

Ive also tried putting a little fuel in the carbs and starting it
Ive tried a little fuel in the plug holes..

I may be overlooking something small so any ideas would be great

Thanks

 

[bigJake]

so you are saying you have good compression, verified spark and put fuel directly in the cylinders and you got absolutely nothing? Don't know how you can have spark and fuel but no fire. try trimming the plug wires back? are you sure you have the correct plugs and they are gapped properly?

 

[gcha1727]

The plugs are new. I also did trim the spark wires back. Im using an inline spark tester and they both look good. I also used the spark tester on my good motor and it lights up the same way.

Any other ideas???

 

[LouDoo]

You say the motor is new, has the motor ever run? You've got fuel spark and air, it should run. How about the timing? Was the motor professionally rebuilt?

I'm at a loss, try PM'ing Dr Honda, see what he thinks?

Lou

 

[bigJake]

yea, I got nothin else. fuel+spark+oxygen=fire. you need a Dr.

 

[gcha1727]

No it was not rebuilt professionally. Long story short, I had a bad crank that I replaced with a used one I bought off ebay. I replaced it myself and im not an expert on the subject. I have seen them apart in the past, but I very well may have done something incorrect.

Also the carbs were bought used. Im not sure how to do the "pop off test" but I did open up and made sure the jets were clear and filters were new.

I struggle with the fuel aspect of this repair.

Is this typically a flooding issue at this point?

Thanks

 

[bigJake]

No it was not rebuilt professionally. Long story short, I had a bad crank that I replaced with a used one I bought off ebay. I replaced it myself and im not an expert on the subject. I have seen them apart in the past, but I very well may have done something incorrect.

Also the carbs were bought used. Im not sure how to do the "pop off test" but I did open up and made sure the jets were clear and filters were new.

I struggle with the fuel aspect of this repair.

Is this typically a flooding issue at this point?

Thanks

that seems to be the logical explanation for why it won't fire, carbs may need rebuilt

 

[gcha1727]

Thanks for the help so far...

I somewhat fimliar with these carbs but still struggle with diagnosing them.

If the carbs are flooding the motor how or what specifically should I be looking for to fix them???

Thanks

 

[bigJake]

Thanks for the help so far...

I somewhat fimliar with these carbs but still struggle with diagnosing them.

If the carbs are flooding the motor how or what specifically should I be looking for to fix them???

Thanks

I'm not very carb literate, I think if it is flooding it could be the regulator diaphram, needles/seat but don't quote me on that.

here is a great step by step for rebuilding carbs
http://www.seadooforum.com/showthread.php?3495-How-to-Rebuild-your-Carb

 

[jhjesse]

RV timing???

 

[gcha1727]

yeah I thought maybe it could be a timing issue... I put the rv back in its original location after turning the motor so the front cylinder was at its highest point...I think thats right but correct me if Im wrong..

I guess Ill try to figure something out with this carb poss flooding...

any other thoughts???

Thanks

 

[Dr Honda]

OK... just read all of this....

As Jake was saying... if you have fuel, spark, and compression... it will start.

Since you are putting fuel directly into the jugs... it would run that fuel out regardless of the carbs. So... the RV timing is either off... or it's not spinning. You said it's in the right place... but is it turning?

 

[gcha1727]

Thanks for all the help...

after looking at the rv again I found that it was not the correct position. It was marked when removed at the top only. When the valve was put back onto that spot it was actually reversed or flipped backward causing the valve to be way off.

Ehhh...