MadManAndrew

My Baja went down while I was running today. Just rolled to a stop while it was still revving. I brought it in and noticed it smelled like something was burning so I pulled out my temp gun and the head measured 320*F. Now, I know they say not to tune by temps on these, but it actually feels like it's running a little rich on the low end and I still hit 320* and completed melted my spur gear down to an unrecognizable piece of plastic. So...any advice here?

378

My Feedback: (4)

I would suspect either an air leak making it go lean or plugged cooling vents. These engines are constantly cooled by fins on the flywheel that act like a fan, however if there's grass in the cooling fins or blocking the intake(It's around the pull start) then they can't get any cooling air to the engine. As for the spur, that could be out-of-mesh gears or it could simply be latent engine heat worming it's way into the clutch bell. Could also be that you overheated the clutch, which in turn heated the spur up.

cheezer1222

My Feedback: (3)

That seems like the most likely scenario, or at least that's what I immediately thought when I read OP's post.

378

My Feedback: (4)

I almost forgot to mention that, seeing as my tenth scalers can't really get the clutch bell that hot, but then I remembered how much the Bajas weigh and how much torque they've got on tap. [&:]

cheezer1222

My Feedback: (3)

Yeah. I also figured that the clutch might be the culprit, because if there was an air leak he probably would have still been able to move the car around, but he said that it just stopped with the engine still revving, so I figured it was probably something with the clutch/spur/pinion.

378

My Feedback: (4)

Well he said the engine overheated too, or at least I think he did. The gist of what I got was his drivetrain let go, then when he checked the engine was way over spec.

MadManAndrew

Yeah, I'm not really worried about the spur, I more wanted to know what the heck was up with my motor coming up at 320*.

378

My Feedback: (4)

Yeah, well as I said check for air leaks in the fuel system and check for plugged cooling passages. The flywheel's got a fan built in that draws air in around the pull start and blows it along the shrouds. It's just like a string trimmer engine in this regard.

MadManAndrew

Thanks for trying, but that does not help at all. I'm aware of how my motor is assembled, I just put the thing together. My carb may not be on tight enough, so I'll go back and try and get it as tight as possible. As I said though, I doubt it could be a leak because it's not running lean, it's actually running slightly rich. My pull start cover is also completely clear, that's why I'm here, none of the normal "check this" are coming up as the problem. I'm gonna go ahead and slap a new spur on amd see what happens. Maybe between my tall grass and the 110* ambient temps it just got to it. Idk.

bbuzzard

My Feedback: (5)

What's your gas/oil ratio mix?

MadManAndrew

Somewhere between 25 and 20 to 1. And 89 octane gas, which, DDM recomends I run 91+ with my stuffed crank, but I'm not having any timing issues.

MadManAndrew

Well, took her out today, tightened everything up, and gave it a good tune, and...still running about 300* at idle, 360* at throttle. I'm gonna email DDM and see what they have to say about.

mooman007uk

if you're running a cmj7 plug, 25-20:1 mix and plug is showing choco brown...so not lean, then nless you've no fins on your flywheel or a grass packed head then i wouldn't worry about it...mixture is the number one factor...and airflow over the head...so one question...you say a gp290...do you have the billet head? those heads are extremely prone to hot running and seizing as they don't run the head/fan shroud which is imperative to cooling these motors

MadManAndrew

Nope, I'm running the regular old head, flywheel, and shroud. I hadn't even thought about checking the plug color, so I'll check it later and if it's a good color I'm gonna take your word and just let it go unless DDM tells me otherwise. Or unless my spur melts again, lol, but I monitored my spur and clutch today and it never got hot with the motor like it did yesterday, so I think it was the clutch that melted it. Thanks for the input.

46u

My Feedback: (3)

Where on the cylinder are you taking the temperature readings? I have found they will very quite a bit from one place on to another. Coarse the heat we been having does not help. Do to my age and heath will not run mine any more till it cools off.

MadManAndrew

I'm measuring in between the first and second exposed fin on the clutch side.