New (to me) XR 750 4

Mad Max in NY

Mad Max in NY

New member
Hello All!
New V-Max 4 owner here. Got a hellva deal this summer on a 89 750/4 for 800 bucks!:sled:
Not a virgin sled but she starts right up. Have some preseason tear down to do. Pretty sure I hear a intake leak.


This should be good,last season I picked up a V-Max600 on the cheap with parts sled. I did a top end rebuild and some custom finish....
Check it out....:3devil-sm


Couple of questions please.....
Jetting, do the Jets really have a number stamped on them? How do you tell what size they are?
Will a Proaction Plus Track fit on a 89 XR750 ?
Exhaust, seems cans are super expensive, are there any mods for a stock muffler or will you kill it?
Top end sounds a lil noisy, worth a set of rings or better do a top end rebuild?

Thanks and look forward to some 'Ridicules Horse Power' sledding soon!
Thanks !
Mad Max in NY
 

Jets do have numbers stamped on them. There is no such thing as an '89 750. They started in '92 and ended in '94 as a 750 and then an 800 from '95 to '97. The pipes and manifolds from an 800 will bolt to a 750 and add some horsepower. Track should fit as long as it is a 121x15x2.52. You could inspect the topend and see what's up. Measure the pistons and make a decision from there. With 4 holes to deal with a top end rebuild can get expensive quick.
 
Welcome to the site! :schild27::schild27::schild27:

Both sleds look pretty sweet! The side panel on your Vmax-4 is from a 1992, the hood looks different. Does it say 800? Hard to tell by the picture. You can download the service manual from the sticky on the General Questions page, but first we need to know if your engine is a 750 or 800. It's an older sled, the engine may have been changed at some point.

Shark
 
rustman said:
There is no such thing as an '89 750. They started in '92 and ended in '94 as a 750 and then an 800 from '95 to '97. The pipes and manifolds from an 800 will bolt to a 750 and add some horsepower. Track should fit as long as it is a 121x15x2.52. You could inspect the topend and see what's up. Measure the pistons and make a decision from there. With 4 holes to deal with a top end rebuild can get expensive quick.
Click to expand...
True that rust man,,, my bad it is a 1992 750... and there was a a hood swap because I have the old hood from the guy.


I wonder about that top end,,, hate to start having fun and the grenade the engine...... I think I will pull it down and give it a look. It was around $100 for the vmax 600 SPI pistons, dang gaskets were as much as the piston kits!
 
mark the shark said:
Welcome to the site! :schild27::schild27::schild27:

Both sleds look pretty sweet! The side panel on your Vmax-4 is from a 1992, the hood looks different. Does it say 800? Hard to tell by the picture. You can download the service manual from the sticky on the General Questions page, but first we need to know if your engine is a 750 or 800. It's an older sled, the engine may have been changed at some point.

Shark
Click to expand...
Thanks for the welcome shark!
Manual is downloaded and Awesome!
1992 750 for sure... I not sure the fella knew what he was doing. Said he was fouling plugs on the PTO side,,, so he bought 4 used ebay carbs! That is why I better check the jet size, could be 800's carbs. It seems to run really rich on the stand,, course it hard to get a good read because I won't tach it out on the stand:beathead:.
There was a hood swap, still don't understand how the hoods get so beat up, too many trees and not enough rider?

Pre season could be interesting, many tips here like the little white tabs to check into. Need to check drive bearing for sure..Will pull the oil pumps to check for shaft rounding,,, any more "Better check that" tips out there ?

BTW I am sooo lucky, the trail is at the end of my driveway and goes for miles. Farmer Brown said OK on the sleds in the field as long as it is frozen and NO ATVs !
 
I hate to be the bearer of bad news but there could be a crank phasing issue. On the 750's there are 2 crank gears that mesh together and spin the Pto gear. It is sounding like one of these gears has slipped out of phase. It is a common occurrence on the 750's. There are numerous threads on here to explain it. It can be remedied but will require a complete teardown. Crank should them be rephased and welded.

Jetting however is 140 mains and 50 pilots stock on a '92. This is too much fuel. You can drop mains to 135 and pilots to 47.5 and be safe. This is stock jetting for 93 and 94. 800 jetting is 143.8 and 47.5 pilots.
 
Still digging into the phase test, I found one here;
http://www.vmax4.com/showthread.php?4700-PLEASE-HELP!!!-BACKFIRING&p=36142#post36142

I did the super crude straw test and it seems spot on. She purrs at idle once warmed up, I read somewhere they sputter when out of phase. I also discovered the shaft runs in front of the engine and think that was most of the noise I thought was top end.

Also found the coil wire looked like the hood slammed on it 500 times. Just for kicks I pulled the main jet out of the origianal carbs and found it to be 133.8. What?This is New York not the Rockies. I know the gas is crap,and dont trust the crude in the oil tank. Praying its not a twisted crank and look forward to a (light) preseason tear down for this season.

Here is video of the 600 I rebuilt last year.

http://youtu.be/qJib1dXqu88

Thanks for the RE's and enjoy the movie!
 
If you have a phase problem the fouling issues will be on the #3-4 cylinders (recoil side) not the pto side.

opsled
 
Mad Max is out of the Barn and in the SNOW!
Runs great (new jet size) and no sign of phasing and sounds really quite!

I would like to add a thermostat so I know when its warm enough to let her Brapp!
Anyone added more then a idiot gauge ?







 
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