Struggling '85 Max at 8K and above..

[Eazrider]

I purchased my '85 Max in 2005, had 18K miles on it, from a dealer/friend in Michigan. It ran like a raped ape, with the following exception, when pulling hard in low gear, it would jump in/out of low gear at about 8 grand or so under heavy throttle. No problem, a shift fork, couple gears and a shift drum and I would be good to go. While I had the motor out, even with only 18K miles, I pulled the head and had the valves adjusted just because. When I put it back together (my first VMAX project) gearbox worked flawlessly. I also installed one of the "kits" that allows V-Boost to kick in at 6-6500 or so. In the past, as the V-Boost opened, the thing would want to stretch my arms out in 1st, 2nd, and into 3rd gear..Now, it pulls hard, but nothing like the feeling that the front end is going to lift in 3rd gear at any moment. Just from observation on the stand, the V-Boost appears start to open at 6-7 grand (I don't have the heart to hold it open any more than an instant in neutral to see if the boost opens completely) The bike had sat for a few months in my shop in the AZ heat, and not having properly drained the carbs, the idle curcuits were gummed up. I disassembled and cleaned them, got all but one operating correctly (#2 cyl). While I had the carbs apart, I pulled the valve covers and double checked the cam timing...No problem, marks aligned correctly. I reassembled everything, and depite the idle issue on # 2 cylinder, took it for a putt...Same deal, a bit flat, surges a bit at about 8500 or so. I have stock pipes, and went up 1 size on jetting, as the story is they come a bit lean from the factory. (I believe I'm at a 55 on the MJs) I have a set of aftermarket plug wires and boots installed, may wet them down a bit and see if I'm getting an errant spark at higher RPMs... Any thoughts on where else I should look. It really chaps my butt that it ran so well before I took it apart, except for that low gear issue...I'm about at my wit's end...

 

[Traumahawk]

Actually what I was told is that they come a bit RICH from the factory. I believe that it was the first year...or 2 years, there was 150's in the fronts, and 152's in the rears. After that they went to 152's all the way around. last year when I dyno'd my bike (I had kerker slip ons) I found out that I was rich, about 2 steps too rich. On a stock Vmax, you should go down one size to 150's, and with slip-ons, drop one more.

Hope this helps.

 

[[email protected]]

I think you mean you put in 155 main jets? That is one size richer than stock.

Max is rich if anything in stock form. 155's mains aren't going to help you any.

I'd go back to stock, at least. Depending on your elevation in AZ, you may want to go even leaner, like 150 or 147.5

 

[dmax1]

Here is a couple of issues I have fixed on my 85 maybe it may help. My bike is stock except for some slip-ons. Have you changed the filter? The tank could have rust in it and you maybe drawing some up and clogging the filter just enough. With the bike off and you first turn the key can you here the v-boost cycle? A carb sync since you had the carbs off and cleaned. Fuel pump pressure test? :confused2: Just a couple simple ideas.

 

[Eazrider]

I had some stale gas in the tank, and pulled the plug from the bottom and cleaned it. Also, I have a 'stone" type filter, and it does not appear to be plugged. I set the carbs up on the bench and adjusted the float levels while off the bike. I ran a fuel line "extension" from the output of the filter over to my bench, and there appeared to be plenty fuel flow. The vboost does power cycle when the igniton is keyed on. I also synced the carbs (which really shouldn't affect WOT, I'm thinking, throttle response, maybe?)

 

[Eazrider]

I was thinking some more on my issue of it running poorly at higher RPMs...If the ignition advance wasn't working correctly and advancing the ignition as RPM increased, I'm thinking that would cause the same symptom..?

 

[jagco1]

Eazrider, I would say carbs something my still be clogging, I had 3 things going when I went through the same thing. I clean to the carbs 3 times the 3rd time boiled the metal parts in lemon juice and then used WD40 to clean parts off this work for me. My bike would stumble around 115 miles in hour... about 600 miles day the road motor started doing almost the same thing again but back firing - gas tank had light rust mixing with the gas I replace the gas tank with a new 1. The 3rd time something happen when I was out of town on the bike would not make it to 75 miles in hour..
I found my gas hose bent right at the wire clamp the back of the carb. Bike runs find now never had any more problems. Not sure if this will help you...

 

[Traumahawk]

Well the advance is electronic....so if it wasnt working...it would probably be really evident. If i remember right the stock ignition really starts coming on around 2800 rpm and only increases about 6 maybe 8 degrees until redline.

Rich is safe....but lean is fast. Are you still running the stock exhaust? If you look at a dyno run with the stock pipes...hp peaks around 8300 rpm...and starts falling off quick.

Sent from my PB99400 using Tapatalk 2