400ex oil pump question

[DirtyHondaEX]

I recently bought an 03 400ex that the top end of the motor was apart on. The guy said it lost compression and the cylinder is scared up. I'm going to rebuild the motor and put in a hot cam. I got to wondering about the oil pump and why the motor burnt up. Could the oil pump be bad or weak? If so do I check with a feeler gauge? Where would I check the clearance? Anything else yall recommend checking? Any advice would be helpful. This is my first rebuild. I'm experienced with carbs and all other stuff on atvs and other equipment, but this will be my first rebuild on one of these. Thanks in advance

[CJM]

Chances are it was jetted to lean, overheated and burnt up. I doubt it had an oiling problem-quite rare on these.

What you need to do is buy the next size piston, a 402 or 406 and get it bored to match and voila you got a new running quad.

The best build is to go slightly oversized piston 11:1 compression ratio, stage 2 hot cam, and put an exhaust on. Also making sure to use cometic brand gaskets-specifically the kind that appear to be rubber coated steel. And you got yourself a really nice and pretty dang fast quad.

The oil pump itself is actually inside the clutch side case if you want to take a look at it. I would also pull the oil tank and check the inline screen on the lower fitting to make sure its not clogged.

[DirtyHondaEX]

Originally posted by CJM
Chances are it was jetted to lean, overheated and burnt up. I doubt it had an oiling problem-quite rare on these.

What you need to do is buy the next size piston, a 402 or 406 and get it bored to match and voila you got a new running quad.

The best build is to go slightly oversized piston 11:1 compression ratio, stage 2 hot cam, and put an exhaust on. Also making sure to use cometic brand gaskets-specifically the kind that appear to be rubber coated steel. And you got yourself a really nice and pretty dang fast quad.

The oil pump itself is actually inside the clutch side case if you want to take a look at it. I would also pull the oil tank and check the inline screen on the lower fitting to make sure its not clogged.
Thanks for the response! The carb was jetted. I'm unsure what size main it has. Would have to look. It has a full white brothers exhaust system and I think he had the air box lid off for more air. I paid $200 for the bike and got extra tires and rims for the rear and the stock headpipe. Not a bad deal. Got to looking, the cam journals got hot and are scortched. The cam is bad worn and the rockers are worn too. I located a used top end in good shape for a good price. It's off an xr 400r. Comes with a cam too. I've heard that using that cam would be like using a stage one hotcam. This true? Oh and one more question, going to 11:1 compression, would I have to run race fuel?? Sorry for the long post. Just thought I would get that all in there. Thanks again.

[Choppers]

Originally posted by DirtyHondaEX
Thanks for the response! The carb was jetted. I'm unsure what size main it has. Would have to look. It has a full white brothers exhaust system and I think he had the air box lid off for more air. I paid $200 for the bike and got extra tires and rims for the rear and the stock headpipe. Not a bad deal. Got to looking, the cam journals got hot and are scortched. The cam is bad worn and the rockers are worn too. I located a used top end in good shape for a good price. It's off an xr 400r. Comes with a cam too. I've heard that using that cam would be like using a stage one hotcam. This true? Oh and one more question, going to 11:1 compression, would I have to run race fuel?? Sorry for the long post. Just thought I would get that all in there. Thanks again.

Race fuel shouldn't be needed with 11:1. Just make sure you jet it properly and you should be fine. Also, the xr400 cam is comparable to a stage 1 but isn't as aggressive.

Goodluck

[CJM]

^ Really cant say it better than that.

I use 93 pump gas no problem on my setup. Jetting is key.

[DirtyHondaEX]

Awesome! Thanks for the help and advice guys! I'll repost if I run into any other issues. I'm looking forward to getting it going