Thread: Triplepiper jetting - HELP!
06-04-2007, 02:22 AM #1
Triplepiper jetting - HELP!
I have triplepiper with Lowell Horning ported cylinders, Novis, V-Force III reeds, 120 PSI Head and R&D CDI.
First carb settings were:
175 - Mains
150 - Pilots
2,3 - N/S
90 - Restrictor jet in return line.
The problem was that motor became to hesitate or stop after immediate throttle opening after idle. More, when running on highs I noticed that I had 7700 RPMs on first pull of throttle, 7800 on second and about 8000 on third.
Then I step by step have changed Pilots from 140 to 155, Mains from 170 to 175, and changed restrictor step by step from 30 to 185 (30, 60, 90, 120, 165, 185).
Nothing was changed!!! Moreover I had fuel pump check valves creased four times even in case of using of 90 jet in restrictor.
I can't understand the reason of this creasing....
Then I guessed that there is not enough fuel in first moment after throttle opening and installed additional 18GPH pumps, one for each carb. And again nothing was changed! I tried to change fuel pressure in return in accordance with Novi's specification (1 PSI on idle and 4.5 PSI on WOT). Only 185 restrictor jet helped me to get acceptable pressure in return.... Why?! Novi's reccomendation is 120 restrictor jet when additional pumps installed but I had 9 PSI on WOT with 120...
Mikuni recommends to install more than one anti-sifon valve when having the same (as seems) problem as I have. I tried to install one valve and two in one carb - without result...
I just can' t understand what is going on with intake... Have an ideas?
06-04-2007, 04:36 AM #2I had fuel pump check valves creased four times
Those plastic diaprams are very delicate, and may be getting damaged during your rebuilding.
06-04-2007, 05:10 AM #3
I changed these valves four times by new ones. I am absolutely sure that nothing was happened with them while rebuilding.
The reason why they are become creasing after short motor working is a part of my question - I just can't imagine why. At first I guessed that the reason is high pressure in return line but pressure is correct after installation of 120 restrictor jet. But the problem is still in place...
06-04-2007, 05:50 AM #4
Are the pumps built on to the carbs or are they seperate pumps?
06-04-2007, 05:59 AM #5
At first I have pumps installed on carbs. The "creasing" problem was with them. Yesterday I added external pumps (check valves of carb pumps were removed, pulse inlets on carbs were blocked).
I have no creased valves in external pumps but the problem with motor and its hesiatation is still in place...
06-04-2007, 09:08 AM #6
- Join Date
- May 2005
Your jetting is way off, excess fuel can cause a backfire that will damage the check valves. Sounds to me like you are drowning that engine with excess fuel
On my 1300 TPP Lowell ported I ran
95 gram spring
90 main jet in the return line.
3 external Mikuni pumps
dual check valves in the metering block
2 throttle arm springs to revent set off during idle
Run a 145 main to play it safe
Forget about that fuel pressure. I see nothing but people going in circles when keeping an eye on that gauge.
With that jetting that you have your performance must really suck and it must be swallowing all of the fuel in no time. BEEN THERE, DONE THAT!!!!
Last edited by Fercho; 06-04-2007 at 09:11 AM.
06-04-2007, 01:32 PM #7
dual check valves in the metering block
Or you mean that you have dual santi-syphon valves?
If first, how fuel comes from external pump to carb if fuel inlet closed by check valve?
Sorry for misunderstanding, my English is not perfect... especially in technical terms...
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