No power under load

[Unruley]

I have a 150 Carbide that I just put anew carb on, a new hipo coil and adjusted the valves. 0.003 intake and 0.005 exhaust. The thing runs great free revving and in reverse, but as soon as it is in forward and under load it pops and farts and won't run over 10 mph. I put it on a jack, and it revs and runs strong in gear. Any ideas on what would cause this???? Thanks in advance for any advice.

Unruley in Michigan

[SLESTAK75]

Welcome Unruley. Did it run okay before the new carb? Just need a bit more background info. Could be a bit off on the valve settings. Could also be air fuel mix or jet issues with the new carb. Is the engine stock or have mods been made?

[Unruley]

Thanks for the reply Slestak. It was running, but only could get about 20 mph out of it before the carb and coil swap. The engine is bone stock. It wasn't running at all a couple weeks ago, and I adjusted the valves and that seemed to cure a lot of the issues. I decided to try a new carb and coil to see if I could get some top end back. I can change the carb back, but was really confused why it seemed to be running great in reverse, and without load on the jack, and as soon as you loaded it up in forward it would stumble and fumble. I'll try rechecking the valves and putting the old carb back on and see what I get. Please let me know if I should be doing anything else. Thanks!

[SLESTAK75]

It sounds like you have low compression. Enough to allow it to run okay until there is a load. Could be a number of things. Usually if this isnt a cured by valve settings it is something inside the engine. If it has been running lean it could have melted the piston. If it was regularly run at top speed high rpms it could have bent a valve. You may check to make sure your intake is tight and not leaking. Try spraying around the intake with starter fluid and see if the idle revs up. If not your intake is fine. Next would be check the compression. If low remove the head and do some examining.

[Masteryota]

Have you tried adjusting the new carb? I know most are close out of the box, but it sounds like it needs more fuel. Is it popping and farting out of the exhaust, or sneezing through the intake? I would try to richen the mix a bit before looking internally.

The reason it runs good under a 'no load' situation has to do with not enough, or too much fuel. Popping or 'sneezing' from the intake indicates a lean condition, and popping though the exhaust generally indicates a rich condition.

[Miamieddie]

Did your buggy run ok before? If so try using the same jets off the previous carb. On the new one and see how that works. If you open up your valve cover to check for bent valves or anything try adjusting ur valves at. .004 on both sides int/exh.

[Unruley]

Thanks for the advice guys. When I checked the compression, I'm getting about 155psi so all seems good there. It is poping out the exhaust so I'll try tuning the carb a bit more or even just put the old one back on. I think I also try to open up the intake valve clearance a bit to see if that changes anything. Is there a good video or instruction sheet on how to adjust these carbs? I appreciate the help!

[Unruley]

Thanks to all. I retuned the old carb and reset the valves to 0.004 intake & 0.005 exhaust. Once I got it fired back up I set the air mixture and reset the idle. Once it warmed up we were able to hit 37 mph. This is by far the best it has ever run. Now I guess I'll start planning for the next steps for bigger & faster!!!

[Masteryota]

Good to hear, I had a gut feeling it had to be in the carb.

[SLESTAK75]

Thats awesome. Always good when the trouble is easy to fix. Good to also get more power. The way to get the best a/f setting is to let your engine get good and warm then while idling adjust the a/f screw. If rpms are dropping turn the other way. 1/4-1/2 turn adjustments allowing 30 seconds or so for setting to settle in. Keep going until the highest rpm is reached. Further turns may cause rpms to start dropping again or stay the same but you want it right at that point where the rpms hit their peak.