About to give up on this thing but figured I would see if anyone in this forum had any ideas with trying to figure out this issue with new 587 short block just installed in the SP from sbt.
Basically, got everything installed and it idles well, but backfires when you try to give it gas both out of exhaust (bit of flame noticed at one point) and pops out of the carb too. I had checked the exhaust for restriction (none). SBT Tech recommended new valve and valve cover. Installed both and timed per spec; no change. New cover actually still slightly out of spec...but anyways...
I turned to focusing on the electrical system as I had put a timing light on it and it seemed to flicker and go dark sporadically at the higher RPMs so figured it was losing spark. Went down the electrical road, checked voltage (13v) at idle seemed ok, unplugged rectifier anyways didn't change anything. Clipped plugs back, no change. Battery was weak so replaced that; no change. Got a complete ebox off ebay (used) installed that no change. I had also cleaned the flywheel as there were some metal shavings in there from the starter. Thought that may have been shorting the stator/flywheel as there was a couple very slight scratched on the stator. Also replaced stator after that; no change. So only thing left on electrical system is flywheel not sure how it could be that. I also ran it with the start stop button unplugged...no change. Same thing with the buzzer line which I have never heard make any noise btw.
Puzzled at this point and looked other directions. Searched and saw that backfire could be caused by lean condition so ran off of fuel bottle. That didnt change anything. Seemed for maybe a moment that it was helping but dont really think so... Changed plugs at the same time, still backfiring... So rechecked the carb to make sure that its pumping correctly and the replacement jet was the right size. Had rebuilt originally and adjusted everything to spec. Pop off was a bit low but hadn't worried about that at the time. Had noticed the high speed screw was out a few turns on rebuild. Its at 0 now.
Next I re-pulled the carb and RV cover. I even found exact TDC to be sure (not screwdriver method). All lined up right on for both valve open and close per the manual. Timing light showed it firing right spot on per manual (in between flickering).
I then took carb off and tore it down again. This time I rigged up a pressure testing apparatus so tested things there. Pop off was low (15 psi or so). Changed out spring to one that got me to like 25 psi so think that is better. Also pressure test on pulse line seemed fine. However, when I did the testing of the fuel in/out lines I discovered a pretty good leak between the diaphragm assembly and the carb housing. I was wondering if that contributed to the possible lean condition at high rpms. Basically the more vacuum at high RPMs would cause it to pull air through this leak... Ended up fixing that leak but it still does the same thing.
I'm running out of ideas at this point. Still think it's odd that the timing light flickers at high rpms but what are the chances that the new ebox is also bad? Any other ideas to look at? Only other thing I thought of was is that I am running without the prop and shaft...would too little resistance here cause an issue? Thoughts appreciated. Thanks.
Ryan
Basically, got everything installed and it idles well, but backfires when you try to give it gas both out of exhaust (bit of flame noticed at one point) and pops out of the carb too. I had checked the exhaust for restriction (none). SBT Tech recommended new valve and valve cover. Installed both and timed per spec; no change. New cover actually still slightly out of spec...but anyways...
I turned to focusing on the electrical system as I had put a timing light on it and it seemed to flicker and go dark sporadically at the higher RPMs so figured it was losing spark. Went down the electrical road, checked voltage (13v) at idle seemed ok, unplugged rectifier anyways didn't change anything. Clipped plugs back, no change. Battery was weak so replaced that; no change. Got a complete ebox off ebay (used) installed that no change. I had also cleaned the flywheel as there were some metal shavings in there from the starter. Thought that may have been shorting the stator/flywheel as there was a couple very slight scratched on the stator. Also replaced stator after that; no change. So only thing left on electrical system is flywheel not sure how it could be that. I also ran it with the start stop button unplugged...no change. Same thing with the buzzer line which I have never heard make any noise btw.
Puzzled at this point and looked other directions. Searched and saw that backfire could be caused by lean condition so ran off of fuel bottle. That didnt change anything. Seemed for maybe a moment that it was helping but dont really think so... Changed plugs at the same time, still backfiring... So rechecked the carb to make sure that its pumping correctly and the replacement jet was the right size. Had rebuilt originally and adjusted everything to spec. Pop off was a bit low but hadn't worried about that at the time. Had noticed the high speed screw was out a few turns on rebuild. Its at 0 now.
Next I re-pulled the carb and RV cover. I even found exact TDC to be sure (not screwdriver method). All lined up right on for both valve open and close per the manual. Timing light showed it firing right spot on per manual (in between flickering).
I then took carb off and tore it down again. This time I rigged up a pressure testing apparatus so tested things there. Pop off was low (15 psi or so). Changed out spring to one that got me to like 25 psi so think that is better. Also pressure test on pulse line seemed fine. However, when I did the testing of the fuel in/out lines I discovered a pretty good leak between the diaphragm assembly and the carb housing. I was wondering if that contributed to the possible lean condition at high rpms. Basically the more vacuum at high RPMs would cause it to pull air through this leak... Ended up fixing that leak but it still does the same thing.
I'm running out of ideas at this point. Still think it's odd that the timing light flickers at high rpms but what are the chances that the new ebox is also bad? Any other ideas to look at? Only other thing I thought of was is that I am running without the prop and shaft...would too little resistance here cause an issue? Thoughts appreciated. Thanks.
Ryan