Thread: GPR running little lean
05-12-2013, 04:51 PM #1
GPR running little lean
I have a fresh rebuild 2001 GPR and running lean on the rear cilinder ,used jetting specs by OsideBill.
1200R Aftermarket F/A's (Flame Arrestors) chokes intact.
- 110 Pilot jets, 1 turn out on low speed adjusters
- 120 main jets, 1-1/2 turn out on high speed adjusters
- 1.5 Needle and Seat, 95 gram spring (Dull Silver) 42-45 avg. pop-off pressure.
Pressure tested the engine at 10 PSI and have a loss of 3 PSI in 5 min. ,that would be in the acceptable range.
Modifications are free-flow exhaust and D-Plate.
Plug from rear cilinder had a grey/white colour after running.
What do you guys suggest? , Richen up the the third carb with the high speed adjuster or do i need another jetting specs ?
05-12-2013, 06:10 PM #2
Is that the only mods. have you done anything to the timing. can you post some pics of the plugs.
05-15-2013, 12:19 PM #3
That are the only mods related to the engine , i forgot to mention running premix en disabled accelerator pump.
I didnīt toch the timing, donīt know if the previous owner did something to it, can it be told from the outside ?
Plug of the lean cilinder fell on the ground and the porcelain broke so i tossed it away, not a smart move now i think of it.
05-15-2013, 08:05 PM #4
seeing the plug would help. there are a few things that can result in the plug color that you are describing. I have seen timing do it and also water getting it from a small crank in the cylinder. it can be mistaken for a lean condition. but you need to make sure it is not lean. I would fatten that carb at least a 1/2 turn and run it and post some pics of the plugs.
05-16-2013, 02:58 PM #5
I will post pics of the plugs after running ,now itīs still a little cold to go on the water but iīll try to run the ski within two weeks.
Carbs are currently on the workbench to install the T-handles i bought from Bill a while ago.
To be continued !
05-25-2013, 03:24 PM #6
Did a new engine pressure test with 6 psi instead of 10 psi ,10 psi seems a little too much what iīve red in some posts.
Pressure holds for more than 30 min so it looks i have a air tight engine.
Installed the carbs with T-handles and fatten up the high speed needle for the last cilinder 1/2 turn.
Only have to drill a hole in the stinger bracket so i can access the last T-handle for adjustment if needed, and wait for the weather to warm up.
Will update after speed run.
06-18-2013, 04:19 PM #7
Today took the GPR to the lake for testing .
Fatten up the rear carb 1/2 turn at the HS needle but still a grey color spark plug .
Fatten up even more the rear carb by 1/2 turn more but still no color change ,and the ski takes of a little slow (i had to play the throttle to rev up).
Plug pics are from left to right ,rear-mid-front .
06-18-2013, 05:58 PM #8
I thought it was 1 psi over 10 minutes. I had a motor I just built leak 2.5 pounds in 5 minutes. I got new crank seals flipped motor over split case put new rear seals in, old inner seal had a small nick in the seal. New ones hold way better. Like 1/4 of a psi in 10 minutes. What was leaking when you pressure tested? If its rear crank seals that can be why #3 is lean. Especially if running it has made it leak more
06-18-2013, 08:26 PM #9
- Join Date
- May 2011
See what others have to say but I would be almost inclined to pull the head off and check #3. Have you compression checked #3. I would expect lean to be more white.
06-18-2013, 08:48 PM #10
- Join Date
- Aug 2006
Grey seems a little too much like vaporized aluminum to me. Better pull the head and check out the piston edges.
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
By dirtyski in forum Yamaha PWC Performance (2-stroke)Replies: 11Last Post: 07-22-2010, 09:32 PM
By fenn in forum Yamaha PWC Performance (2-stroke)Replies: 7Last Post: 07-06-2010, 06:47 PM
By 98gsxl951 in forum Yamaha PWC Performance (2-stroke)Replies: 0Last Post: 05-24-2010, 08:50 AM
By homebrew in forum 4-Tec PerformanceReplies: 17Last Post: 02-14-2010, 03:37 PM
By tsho in forum Yamaha PWC Performance (4-stroke)Replies: 3Last Post: 12-08-2009, 08:22 AM