Mileage problem

[dmoffitt]

A few months ago I purchased a 99 RSV with 49K on the clock that had been parked for several years. I have removed and cleaned the carbs, new plugs, fresh oil. The bike starts first turn without the choke, carb balance is near perfect at idle and at higher RPMs, compression on all cylinders is well within specs and the bike pulls strong.

The problem is that I am getting a consistent 22 miles per gallon over the last 400 miles.  Where do I look now?

[RDawson]

First thing I’d check is to make sure it’s running on all 4. These things pull amazingly well on 3 cylinders. Fire it up cold and see if all 4 pipes heat up the same, I use an infrared thermometer to check em. 

[etcswjoe]

That poor of a mileage I would look for a leak as well, if the PO put in an aftermarket fuel pump it may be leaking by.

These are based on personal experience only. 

Edited August 9, 2023 by etcswjoe

[dmoffitt]

17 hours ago, RDawson said:

First thing I’d check is to make sure it’s running on all 4. These things pull amazingly well on 3 cylinders. Fire it up cold and see if all 4 pipes heat up the same, I use an infrared thermometer to check em. 

Hmmm. I just bought an infrared thermometer last week! Wohoo! I get5 to use it for something besides just pointing at the cat!

[dmoffitt]

I just went out and checked to see if it was firing on all four cylinders by taking a temp reading on each cylinder. I removed the dog-bones and took the measurement from the head, next to the spark plug. At idle, all cylinders read within 10 degrees of each other up through 180 degrees as near as I can tell.

 

I tried raising the RPMs but getting accurate readings while holding the throttle open was problematic at best. But I'm pretty sure it's hitting on all fours.

[RDawson]

Any possibility of brakes dragging? 

[Marcarl]

Maybe recheck your numbers from scratch.

[dmoffitt]

going to be out of pocket for a couple days, will update when I return.

[dmoffitt]

I'm back with new numbers.

I pulled the plugs and did a compression test, all cylinders were 120 to 125 PSI,

Reinstalled the plugs and checked carb balance. All carbs indicated within 1 inch of each other at both idle and ~2500 RPMs. Although the readings were even, they were all lower than I would expect to see @ 10-11 inches at idle. Vacuum would increase to 15-18 inches at 2500 RPMs, deceleration vacuum would jump to 20-25 inches then settle back to 10 inches.

The only other thing I see, take a look at the pic. Both cylinders 1 & 2 look like the plug on the left, cylinders 3 & 4 look like the plug on the right. This is after about 400 miles since install.

[Marcarl]

In MHO the left ones are running rich or not getting a complete burn. The ones on the right look good. So that could be part of the issue, but I think there is more hamburger in the pattie, somewhere.

[dmoffitt]

Reading through the Service Manual, it says that the "Compression Pressure" should be 15.2 Bar (1520 KPa). According to my handy, dandy converter that works out to 220 PSI. That can't be right can it? Or are they talking about something else?

[Marcarl]

15 minutes ago, dmoffitt said:

Reading through the Service Manual, it says that the "Compression Pressure" should be 15.2 Bar (1520 KPa). According to my handy, dandy converter that works out to 220 PSI. That can't be right can it? Or are they talking about something else?

That's what I see as well. Now that is at 175rpm with throttles wide open. 220 makes sense I think.

 

[saddlebum]

#1 did you remove the air cleaner

#2 Did you make sure throttles are wide open

#3 Make sure you have optimum cranking power add a boost battey or good charger

Manual states 216 psi @ 175 rpm. This is for a fairly new engine and will  reduce as the engine ages. Most used engines run between 110 and 130 PSI and no more than 20% between highest and lowest cylinder.

Last time I checked mine they were 98- 120 psi and the engine runs like a dream. In any case I would not loose sleep over the readings you are getting and look more into fuel control for your rich fuel conditions.

[videoarizona]

I'd take the carbs off and check the floats. Left side is real rich and that can easily be float settings on left side carbs. 

To add to that, the float seats may be dirty from sitting and allowing to much fuel into bowl. Or not allowing float to move properly. 

Regardless, go over 2 left carbs with a fine toothed comb ( so to speak)

Edited August 14, 2023 by videoarizona

[dmoffitt]

Thanks all for the ideas. I guess my next step is to remove the carbs and verify everything. If someone has a hammer handy, I would rather smash my thumb.

[videoarizona]

If you haven't removed the carbs yet, let me say that it's not that hard at all! I did it twice... With nothing more than reading the posts from guys who have done it on this site. 

It's just time consuming. I think it took me 2 hours first time. Stopping to take notes and pictures so I could get it back together. When I got the carbs out, I thought "that really isn't that hard". 

Just saying...