I have a 1998 425 Magnum with 4,000 miles, it cranks good and idles fine but....when you accelerate quickly the engines sputters (dies) down and almost stalls then will rev up a little and dies down again. I can hear popping (back firing) in the exhaust while throttle is held open. The things that I have tried and checked....if you crack the choke a little the engine will die, adjusted valves, checked compression( reading was 115psi), did a leak down test and according to the gauge the leakage was low, changed spark plug, removed the muffler and no change. Also, removed filter no change but I have found that if you spray ether in the air box the engine will pick up or remove air box all together engine revs fine. With engine at high rpms putting the air box with no filter back on the carbureter the engine quickly starts bogging and sputtering. I also dissassembled carbureter and throughly cleaned and replaced float valve. Thanks for any advice Phillip

 

Try moving the "e" clip on your needle down one or two slots. This will increase fuel delivery from 1/4 to 3/4 throttle.



SB.

 

the popping is usually because of a lean problem. sounds like u have an air issue. when u take off your air box your allowing more air meaning when your the air box is on it should be richer then when its off. when you looked @ your carb. when you had it apart, did the slide, needle or anything esle looked worn out. i have seen it happen w/ alot of miles, but not very offten.

 

These are a couple of things I forgot to mention, I also replaced the metering needle, the spring on top of the diaphram(thought it might have been weak) but no there was no change. I have tried moving the clip up one notch because the spark plug was fouled I thought it was running rich but it made no difference. I will try moving the clip down and see if this helps. Is there anything else in the carbureter or electrical that would cause this?

 

Look at the camshaft, a 500 ho will bolt right in.

 

Check the ETC(electronic throttle control) adjustment on the throttle.
Too much play in the cable will cause a "misfire" problem.
Listen careful and if you can hear a switch "click" as you pull the throttle off idle you need to adjust it.
The way it works is the reverse speed limiter is tied to the throttle so if the throttle cable sticks and you let off, it will "limit"(some times kill) the engine.
Read your owners manuel to adjust.
Hope this helps

 

Same problem as one i repaired. Exaust lobe worn completely off the camshaft. It should be same height as the intake lobes. Easy to check and install new camshaft.