BlackMax Probs.

[chadbenton]

I have an 88 blackmax 150 xr2 with a recurring problem. Twice in two years now it will run good. Then I take it to the lake and it happens, my tach shows double at idle, around 2000 and it runs like a dog, will not gain any rpm at all and can not pull itself out of it by going to wot. Pulled plugs and they are pretty fouled. But, not sure where to go from here. It might run perfect next time out. Any help would be greatly appreciated.

 

[CharlieB]

Re: BlackMax Probs.

You have to start with the basics.

Test Compression, at least 100 PSI and all cyl within 10 psi of each other

Test spark on each cyl, 7/16 gap, must be bright blue 'crack'

If both of these check then you know that the engine is mechanically sound and you problems most probably lie with the fuel system.

Make sure the carbs are spotlessly clean throughout ALL internal passages, floats set correctly, throttles linked and sync'd per the service manual.

Skip any step and it won't run right.

 

[chadbenton]

Re: BlackMax Probs.

Ok, did a comp. check when I got home from the lake, and all cyl. were right at 115psi. So, that all seems good. Did not check actual spark, but can do that tomorrow. Just really curious about the tach. showing double or so, and being intermitent. Has you seen this before, possible rectifier issue or even stator.

 

[CharlieB]

Re: BlackMax Probs.

If the engine runs up to WOT and the battery stays charged, then the stator and rectifier are both working, most probably the tach is failing.

HOWEVER, since there is NO RETURN on electrical parts you should test everything to be sure.

Disconnect the rectifier and Ohms test the yellow stator leads and the rectifier following the proceedure in your service manual. Reconnect and test battery voltage with the engine OFF, then again while running at 2000 RPM, if the running voltage is greater then the charging system is functioning. Then you can safely conclude that the tach is defective.