The saga continues-compression done/plug pics

[davesax36]

Before I start... 5300 miles on bike. Sat from '05-'11, when I bought it. It was obviously under a tree or something for a lot of that time.

I've been getting 20 mpg for all three tanks of fuel I've put through my max.... I know that's not right. Everything seems to run smoothly, but I don't have instant power on WOT at 3k. It goes, just not as soon as I'm sure it should. Today I picked up the compression gauge from O'Reilly and got to work. Pulled my plugs to see what they looked like. I was expecting terrible things, but i got the attached. They don't actually look too terrible to me. They are in order from R->L 1, 2, 3, 4 (just the way you'd see them looking at the bike from the front).

Then I hooked up the compression gauge. I grounded the plugs and thumbed the starter.

1- 145 (low, but not bad!)
2- 137 (lowER, but within 10% so I figured maybe the gauge was just going to read everything low--carbon deposits/whatever)
3- 115 (bad)
4- 125 (bad).

It took about 10 cycles to get to these numbers, but I decided to not stop until the needle stopped. I've never done compression tests before, and it's possible I did something wrong- didn't tighten the insert enough (doubt it) or some other noob mistake. I let the gauge sit for a couple minutes on each one to do a sort of leak down test and the pressure stayed up well. I don't know how long that's supposed to take, though. I'll probably go try this again on the two lowest cylinders later today to see how long it takes to lose pressure. That was a lot of cranking.

Carb number three (right rear sitting on bike) has been visibly wet after riding, but doesn't pump anything up through the wrong tubes when idling or warming up. I can't really tell if it's gas or not, but what else could it be? It's certainly not oil or coolant, so I'm going with leaking fuel. I have not figured out when it gets wet and it does seem to be only below the coasting enrichener. None of the other look like that.

Is it possible that the low compression in this cylinder is also causing low enough vacuum (carbs sync fine/idles appropriately) to cause fuel to build up and run all over the place? I think a direct leak would explain my super low mileage. It smells rich at stop lights SOMETIMES, but I feel like a change in wind direction could do some of that. I don't think I ever smell raw gas and it's not enough to drilp when I get home. I have other unrelated drips, though.

The motor is coming out in the next couple weeks for transmission swap. I'll get back with Sean to see if I can get the valve checker kit so I can complete that.

I know somebody will write a one sentence answer that solves all my problems, costs nothing, and gets me free tickets to Disney World. Thanks for your patience reading about all my screw-ups and offering sound advice.

 

[RempageR1]

Did you do the compression test at WOT? If not, you should.
If still low, squirt a little oil on top of the piston and recheck. If it goes up, rings might be worn. It can also be caused by worn valves or something simple like valve clearances. A little low isn't really going to hurt you though.....

As for your low mileage, that sounds really bad. I`m doing about 37 MPG. Since you are doing a transmission swap, it seems a good time to overhaul the carbs. When the max isn't used for a long time, gunk clogs up the jets. Also, the diaphragms can dry and crack. There`s tons of information about this on the forum so just do a quick search.

Good luck!

 

[davesax36]

Crap! I knew I'd forget something. I'll go pull stuff apart and do it WOT. I hope that increases my numbers. It could be that the battery was getting tired, but I don't think that effects compression. The carbs are new. Danny just built them for me. All stock vmax parts inside some Venture carbs. Maybe I'll take one of my crappy tanks and get it cleaned and recoated even though I don't think things are getting gunked up since it's running smoothly.

 

[davesax36]

Ok. Redid it the RIGHT way...
1- 165
2- 150
3- 160
4- 150

Not sure what's up with 2 and 4, but they're bang on the same. Range is barely acceptable, but certainly not excessively low, I think. Maybe I did pump something into number 3 that's making it back up. Would a stuck float behave like this and cause a 50% drop in mileage? That seems like a lot of impact for one carb. It needs choke to start when cold, so that should mean that it's not too rich. Always smelled rich at idle, but that doesn't seem abnormal, either. I really don't want to dismantle stuff any more than I have to.

 

[mr.maxx]

how many turns out on the pilot screws? are they all set the same? did you do a carb sync?

 

[davesax36]

Just synched. Super steady on my Carbtune. I haven't fiddled with the A/F screws because Danny ran them on his bike before he sent them to me and got great mileage....I really don't think they worked their way out during shipping or install.

 

[06VMAXIMUS]

Upper left plug in pic looks darker than other 3. Maybe not getting good spark there....especially if carbs were just redone. Leak down test is done differently than a compression test, with a different gauge.

 

[davesax36]

I'm gonna look for the parts to do the leakdown. I switched that dark plug to a COP. I thought that would give better spark. I'll try another one and see if that helps. Would weak spark allow incomplete burn and cause mileage that bad?

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[06VMAXIMUS]

Best way to do the compression test is: Make sure the battery is fully charged, remove and ground all 4 plugs to the engine, install gauge and test each cyl while holding the throttle wide open with the choke off, document results. Now that you know what the compression ratio is in each cyl, you can squirt a LITTLE oil in each cyl (as mentioned above) and redo the test to see how much it increases. This will tell you if the different values mean that the rings aren't sealing or if a valve is possibly slightly open...ie: burnt, bent, or badly out of adjustment. Weak spark can and will make an engine run like poo. Let us know how you make out.

 

[davesax36]

I'll put it on the battery tender today and try the added oil bit tonight if I can. I'm assuming that if added oil makes no difference, I have to go to the next step (leakdown), and added oil increase means try new plugs first?

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[06VMAXIMUS]

When cranking the engine over, you want it to have a good strong spin. Crank it until the needle stops at its highest point and record the reading. When adding oil to the cyl, only add a few drops....you don't want to put too much in there. If the oil doesn't make a difference, then you probably have something going on with the valves. I think your problem probably lies with a weak spark, but lets see what the 2nd compression test says first.