1978 Cyclone 340

Jack Frost · Post by **Jack Frost** » Tue Feb 06, 2007 10:59 pm

Just wondering if any of you guys could help with this little problem? 1978 Cyclone 340 fresh rebuild, new pistons,new seals,new gaskets,rebuilt carb,new cdi,new coils,new plugs,clean tank,new fuel lines and filter. Problem is the top end spits and sputters but won't wind up to it's full potential. Starts no problem,idles fine,speed up to about 35 to 40mph no problem. Then when you hit about 40 + mph the sled hesitates and stutters till you drop back down to 40mph and below. Timmings good so is it the stator and how do you test it? Any help would be appreciated.

Regards. Dave

:blink:

harleysportster · Post by **harleysportster** » Tue Feb 06, 2007 11:17 pm

Dave,
Check this out from the FAQ section.
http://z12.invisionfree.com/jdsleds/index.php?showtopic=1587
Do you have a tach on the sled. What color are the spark plugs. What condition are the primary and secondary clutches.

Jack Frost · Post by **Jack Frost** » Tue Feb 06, 2007 11:34 pm

Harley are you saying that I get a JDM-74 tester to try and pinpoint the problem? Or are you saying my cdi is bad? Clutches are both rebuilt,has tach, plugs are blackish brown and sled seems to be running on one cylinder but only at top end.

Dave.

:blink:

harleysportster · Post by **harleysportster** » Tue Feb 06, 2007 11:41 pm

Dave,
Read all the info that I pointed out in the link. Between what I provided and the cheater tests that Rich provided, you do not need the JDM-74 test equipment.

harleysportster · Post by **harleysportster** » Tue Feb 06, 2007 11:47 pm

You should also test the spark plugs with a in-line spark tester with the engine running.
http://www.harborfreight.com/cpi/ctaf/disp...Itemnumber=4445

Jack Frost · Post by **Jack Frost** » Wed Feb 07, 2007 12:01 am

Harley I have tried 2 different cdi boxes, 3 different sets of coils, 3 sets of plugs, 2 carbs and 2 fuel pumps..... All with the same outcome no top end... The one link that you posted only explains how a JDM-74 tester works and it's adaptors.

Dave.

harleysportster · Post by **harleysportster** » Wed Feb 07, 2007 9:50 pm

Dave,
I posted the wrong link. This is what I meant to post:
http://z12.invisionfree.com/jdsleds/index.php?showtopic=491
Try this also:
A "quick and dirty" check for the Prestolite CDI when the engine runs but seems to lack power or fowl plugs is to turn until #1 is at TDC (aprox...don't need to use a dial indicator)...then mark the inner clutch surface, using with a black marker, with a horizontal line aprox 1 inch long. Turn the engine 180 degrees and mark the inner clutch surface with a vertical line. Now, attach a timing light to #1 plug wire and start the engine. If you see only a horizontal line, the CDI is fine; if you see a "+", the CDI has failed. You see, each cylinder is to get it's own firing spark, but one mode of pack failure is when the circuits break down and connect, reducing the voltage of each ignition spark.

Another tip is to always have a spark plug installed in the plug connector when turning the engines over...these CDIs had such high voltage that if a path is not supplied to complete a circuit...the voltage often finds a path not intended, damaging the CDI.

Jack Frost · Post by **Jack Frost** » Fri Feb 09, 2007 9:21 pm

Thanks for the info Harley.... will try your tests this weekend when I'm not sick with this head cold the kids gave me. Picked up a stator just in case.

Dave

Jack Frost · Post by **Jack Frost** » Mon Feb 12, 2007 11:01 pm

Harley checked the cdi again and it's ok.Checked the coils and they are ok......then pulled the stator out and it had a wire that was breaking off.Put the new one in and she ran like a Deere again.

No more top end let down. Just in time too because we are going to get a wack of snow starting Tuesday afternoon here in southern Ontario.Thanks again.

Regards. Dave

harleysportster · Post by **harleysportster** » Mon Feb 12, 2007 11:07 pm

Great to here the good news.