Fluctuating Vacuum Reading 99RSV

[trandeod]

I ran a tank of of Chevron mixed with a can of Seafoam thru my carbs and then two more tanks with a 1/2 can then let it set for a week soaking while I ran out to Ft Worth. Today it was running better but still idling rough. I tried to get a vacuum reading and the hand was fluctuating on all the cylinders so bad I couldn't get a good reading. Also my right rear exhaust pipe at the block was reading a temp of around 600 deg and the rest were 250-300. Most of my tools and my manual are in Tennessee and I'm basking here in Florida acting like a Snowbird. I can't remember what causes a vacuum to act like that. Any suggestions? Also, can the 600 degrees on the right rear cylinder do any damage? Would appreciate any thoughts. Thanks.

[MiCarl]

The vacuum does that.

 

You need a restriction in the line to damp the fluctuations so you can read the gauge.

[Guest scarylarry]

Hey I know you have to have inserts on the carb tune or they will go haywire, the exhaust temp seems like a float could be sticking best I can remember here..

I would seek out ol' v7goose, he has never steer me wrong...

[friesman]

My Carbtune came with plastic inserts to restrict the airflow so you dont get the bouncing, just cut the rubber tubes and insert .

 

Brian

[wes0778]

If you are using regular vacuum gauges, you need to go by a store that sells aquarium supplies. Pick up a brass air line valve for each gauge. This way you can restrict the hose to the gauge enough to dampen out the pulses, so the gauge needles give a readable result.

[V7Goose]

I ran a tank of of Chevron mixed with a can of Seafoam thru my carbs and then two more tanks with a 1/2 can then let it set for a week soaking while I ran out to Ft Worth. Today it was running better but still idling rough. I tried to get a vacuum reading and the hand was fluctuating on all the cylinders so bad I couldn't get a good reading. Also my right rear exhaust pipe at the block was reading a temp of around 600 deg and the rest were 250-300. Most of my tools and my manual are in Tennessee and I'm basking here in Florida acting like a Snowbird. I can't remember what causes a vacuum to act like that. Any suggestions? Also, can the 600 degrees on the right rear cylinder do any damage? Would appreciate any thoughts. Thanks.

Two big questions for me, but probably not material either way. You do not say what tools you were using or explain what "the hand" would be; however, as others have already said, fluctuation on a vacuum gauge is normal.

 

Any single cylinder vacuum reading will have huge pulses at idle speed on ANY engine unless there is major restriction in the vacuum line. I have explained this in detail in older threads if you need the mechanics behind it, but the point is that this does not sound abnormal.

 

The temperature readings are probably wrong. I do not know what tool you were using, how you were using it, or how careful you were being to be EXACTLY the same on each cylinder. HOWEVER, in my experience trying to take the same types of readings with a good quality hi-temp IR thermometer on this bike, it is virtually impossible to get reliable readings this way. Even with a laser sight on the tool, very slight movements in the aiming spot of only 1/4" produce wild variations in temperature readings. Furthermore, the rear cylinders always read much higher than the front - two reasons for this: The front cylinders run much richer, AND it is not possible to get the IR readings from the exact same spot on the headers.

 

So my point here is that I wouldn't get too worked up over the temperature readings unless you have compared them side-by-side with another identical bike. I would put a lot more faith in the fingertip test on a semi-cold start for pilot jets, and an engine chop/plug read for main jets at 3,000 RPM.

Goose

[trandeod]

I appreciate the advice from you guys. I used a single vacuum guage borrowed from a friend and an Actron IR temp guage. I am mostly concerned about the temp on the right rear cylinder. I bought the bike after it has been sitting for long periods of time. It's a 99 model with 12,000 miles, so you know it hasn't been used a lot. I'm vacationing in Florida in a 5th wheel RV and most all my tools etc are in snowy, cold Tennessee. I guess I won't ride it extensively until I can get it home and clean the carbs etc. Thanks again for replying. Hey Goose, I sure spent some quality time in Ft Worth last week, love it out there.

[V7Goose]

A single vacuum gauge is not much use, IMHO, even if you buy an aquarium valve to use as a restrictor. While it is technically possible to check just one cylinder at a time, decide which one to take a wild guess on making an adjustment, then recheck them all before trying it again, If you actually care about getting them within spec, you'd probably run out of gas before you could ever get everything in sync.

 

In fact, I personally think it is not worth the effort to even try a sync with just two gauges instead of four. I know we have a few people here who feel they are just fine doing a sync with only two gauges, but there is just too much interaction between all the carbs for me to be satisfied with it. In an emergency I could get them reasonably close that way, but I generally would not waste my time with any vacuum reading unless I had a tool to read all four at once.

 

As I said above, I don't think you should worry about the temp readings you got - I do not believe they are correct. I think there is almost no chance that one cylinder on a water cooled engine could be running that much hotter than the rest. If it really is, a plug reading between the two rear cylinders should show an obvious problem. But of course it is always safest to not use any vehicle when in doubt.

Goose

[BOO]

It has been some years ago but we use to race snowmobiles. Keep in mind I'm talking about 2 cycle engines. Seems to me thought that we would blow a hole in the piston at around 700 degs F. If in fact your motorcycle is running 600 deg that would be very hot and like Goose I would tend to believe that is not an accurate reading.

Usually when you have a carburetor plugged or somewhat plugged the cylinder runs cooler than the others. I'm talking about our 4 cycle bikes now.

I think you doing the right thing though and not riding the bike until you can clean the Carbs.

The bike I now have had sit for about 9 months when I bought it. I drained the whole fuel system before riding it but there wasn't much in it that I could see.

Couple of years later I had a float stick and had to take them apart again and again I didn't find anything in the system but it was fine when I started it again.

It's not a real big deal to take them apart and there are some real good instructions on this site.

Note: That 700 deg reading is a little relative, it depends a lot on where the probe is inserted in the exhaust system but as I recall the probes where only 2 or 3 inches from the cylinder.

Good Luck,

BOO

[wes0778]

Just a thought, but I wonder if the carbs are so far out of sync that the "hot" cylinder is just carrying the load? Get at least one more vacuum gauge and check the vacuum readings on #3 and #4, then #1 and #2 then #2 and #4. Bet you will find a big difference between the "hot" and "cold" one.

 

Also see

 

http://www.venturerider.org/forum/showthread.php?t=258

[MiCarl]

Just a thought, but I wonder if the carbs are so far out of sync that the "hot" cylinder is just carrying the load? Get at least one more vacuum gauge and check the vacuum readings on #3 and #4, then #1 and #2 then #2 and #4. Bet you will find a big difference between the "hot" and "cold" one.

 

Also see

 

http://www.venturerider.org/forum/showthread.php?t=258

 

This is a good suggestion. I doubt that 600 is too high for an exhaust header, the 250-300 is probably low.

[Condor]

After that much Sea Foam thru the system you probably need new plugs. You may have one or two that are fouled and the fuel is burning in the exhaust stream causing the high temp readings. Also probably what's causing the rough idle??? My