717 won't run

[adamzpop]

Just put a 717 in my '95 GTX..had some good folks here tell me the electronics were compatable. The only thing I knew about this 717 was it had good compression.I quirted a little fuel mixture in the carbs and it fired right up but after reving it up a few times it would die right out... went on like this till the batt was dead.Here is what I checked.

Mag to PTO carb connections are correct

It's getting fuel...feed and return lines were full uf gas when I pulled them off. I also blew back through the lines to make sure there were no restrictions

internal fuel filters are clean

pop of on MAG carb is 42. PTO is 38

Highy speed ajuster is 0.Low is 1 1/2

all carb ports are clear


Any input is much appreciated

Thanks

 

[Bills86e]

Remove the fuel return line, spin engine, is any fuel coming out? Do you have single or dual carburetors? You have both spark & comprssion if it ran when you put pre-mix gas into the carb(s). Narrows it down to delivery or carb failure.

 

[adamzpop]

It is dual carb. tomorrow I'll try the the return line test you suggested . The line was full of gas when I pulled it off so I figured fuel was moving through the system. Thanks a lot for your input..will post results

 

[Bills86e]

What year model did the 720 dual carbs come from? Mikuni 38's have 3 arrestor holes
40I carbs have two, slanted.

pop off's should be same or within 1psi, the mag is def too high. I'll wait.

 

[adamzpop]

I don't know the year.The guy I got it from didn't know it's history.The carbs are 38's.I will try and mach up the pop off pressures tomorrow,...what do you think..35psi? Thanks for trying to get me straight. I really appreciat the good people on this site who are willing to share there expertise

 

[Bills86e]

You need to figure out if it needs more, or less fuel going into the motor when trying to start it, then adjust the pop off for what it needs to fix it. If you need to use the choke, it needs more fuel, if you need to hold the throttle open or cracked open, it needs less fuel.
Pop-off is the measurement of the point where atmosphereic pressure overcomes the fuel draw vaccum of the carb. The entire regulator chamber is nothing more than a big check valve. It is the step between the fuel pump, which is providing more pressure than the carb needs to deliver, and the jets, which meter a fixed amount, within a certain pressure range. The regulator chamber is in place to maintain that pressure range.
The year & model COULD have given us specs. Now you are putting the possible 1995 717 model XP (5857) x-4 hull, into a larger (more water to push) similiar to
a say 96 GTI. You may have little inky-dink 1.2 jets and need bigger, and a spring
gram to get you to the weight plus barometric range jet.
Basically, if it is dripping when you look in there, you need more pop-off.
I think the 96 SPX may have had the dual 38i's. My book with the yr & weights have disappeared from my shelf, maybe Another Tech here can chime in. now that I remember that GTI had single carb=no help. the '95xp
had the duals, 137 main jet 67.5 pilot hi-0 low-1 3/4, 1.5 jets. 95 gr silver.

 

[Bills86e]

OK. Remember to look see if 3 or two, this will help determine carb body 1 or 2, and the type. (round-square). This is an out of ordinary determination, as jetting, PO, needle & seat sizing vs weight-HP.

 

[adamzpop]

The carbs are 38I's type 2 (square body)
Thanks again

 

[adamzpop]

ok.I set the pop off to 35 (give or take 2 psi)on both carbs...squirted some fuel in the carbs and she fired right off and died right out.when the engine is running fuel will pump out of the return line.Fuel will not flow out of the return line by just cranking the engine over. one thing for sure..the engine is not getting fuel. Do the pump valves on these things lose pressure over time. At this point the only thing I can figure is the pump is to week to pop the needles.Thanks for the help

 

[seadooya]

bypass the fuel selector and the inline filter. Run a fuel line from the "res" fitting off the tank, right to the inlet fitting on the carb. If you have compressed air, shoot it into the "pulse" fitting, to clear it out, but not too much pressure. Then compress air ALL thru the carbs lsa/hsa housings, jets,..etc, meaning, pull carbs again. If you didnt mess with the "spring" in the n/s assy, then your pop-off should be good, make sure the "tang"/needle arm spring, is level with the inner body of the carb.

 

[adamzpop]

I won't be able to work on it again until Monday but am anxious to try your sggestions.This thing is drivig me crazy!Thanks for the help

 

[Bills86e]

Do you have fresh gas? It can go bad in 3-4 weeks. Here are some specs that may be helpful in reseaching:
1995 GTX model=5863 weight=485lb prop=10/22 engine=657X-80HP MAG270500259 PTO270500258 BN-38I (SB) MAIN-132.5 PILOT-75 NS=1.5 spring=270500242(D) PO=19-35 LOW- 1-1/4 HIGH- 1/4. A 720 (717) has large oval intake case ports, the 657x ports
intake round ports, you can dremel them to fit if needbe. 717=85HP stock.

 

[Bills86e]

I won't be able to work on it again until Monday but am anxious to try your sggestions.This thing is drivig me crazy!Thanks for the help

I have a scheduled "same as" project in may. Keep us informed of final results!
I can use your thread as guide. It will be a single carb conversion, maybe
I can leave the RV assembly with dual 38I's in & hooked up as a unit.

 

[Bills86e]

I won't be able to work on it again until Monday but am anxious to try your sggestions.This thing is drivig me crazy!Thanks for the help

There is more often than not a problem inside a carbureator, typically, those problems are water sitting in the carbs rusting up stuff, needle and seat valves that are stuck shut, diaphrams that are stiff old and hard, sometimes vulcanized ( glued ) to the diaphram cover plates so they can barely move inward to open the needle valves when necessary, or just partially open the needle valve which reduces fuel flow, gasoline/oil varnished internal carb parts, clogged internal filters, bad fuel pump diaphrams, ect.ect.ect.
Then to add to the list, water in the bottom of the gas tank, or a gooey mess of hardened pre-mix oil thart seperated from the gasoline, a clogged up fuel selector valve, rotten fuel lines and last but not least, the wrong style inline fuel filter. The one small fuel pump that feeds two thirsty 720 carbs cannot put up with any restrictions caused by the wrong style inline fuel filter. Bills86e

 

[adamzpop]

i went through the carbs and everything is free moving and all ports are clear.I was thinking of removing the mag carb,removing the needle cover and with the pulse and fuel line still connected see if it pops off while cranking the engine.I have another question about the fuel circuit. With the feed and retun line disconnected and I blow into the return line it seems fuel shoud be forced out the feed line. The tank pressurizes but no flow out the feed. Now when I blow into the feed line I can here bubbling in the tank....not sure what is going on there but as you mentioned there may be some restriction in the feed line.I feel I'm getting close to solving this.Thanks for hanging in there with me.

 

[Bills86e]

Find/remove the fuel bafel two lines out ON & RES (180* apart on the four nipples)that go to the selector and with supply line at carb removed, air chuck thru those two ( mark at least one of them for orientation) if nothing comes out, disconnect the fuel out line from the valve and retry, ect,ect.
Turning it from ON, to RES, helps, but if its aluminum, replace it with a plastic one, this will not corrode & clog.

 

[adamzpop]

Ok I'm back at it after the Easter holiday.Today I disconnected and checked the entire fuel system. The selector had a little leakage between on and res so I ran a line straight from the res line on the tank baffleto the carbs and have good fuel flow.fuel is pumping out the return line.I took the carbs apart...again, and all diaphragms,ports,jets and pop off look to be set and working...put the carbs back on gave a shot of gas and it started right up and died right out.If I choke it heavy it will run. When the choke is let off I can rev it a few times (LIKE IT STORED SOME FUEL SOMEWHERE) and then die right out unless I hit it with the choke again. So apparently she's not getting enough fuel. I can not think of anything else to check...could it possibly be a rotary valve problem?

 

[Bills86e]

Have a little bottle of pre-mix handy when you start it up, if it startes to die dribble a little in the carb(s). if it continues to run, but quits after it consumed, its fuel related to either fuel delivery & freshness, or a carb & pump&pulse problem. BR8ES
gap .021.
Next, buy two clearglass spark testors to watch spark while it runs then dies = Elect.

 

[adamzpop]

I might not be the bigest fool in the world but I feel like it.When I bought this thing it had about 2 gallons in the tank so I added 2 more gallons to it. When it wouldn't start I siphoned off 1/2 gal for my pre-mix squirt bottle. The engine started right up when i squirted this in the carbs so I never even considered bad gas. Well apparently the gas was good enough in this quantity but not in the controlled amount flowing through the carbs. As a last resort I emptied the tank and used fresh gas....runs like new.Thanks for hangin with me Bills86e. This has been a good frustrating education and I can now disassemble,clean, test, adjust,reassemble and install these carbs in my sleep

 

[adamzpop]

unfortunatly this was a premature celebration.I ran the thing on a hose for about 2 min and if ran great. Yesterday it went right back to the same problem. The thing will only run on full choke or if I keep squirting pre-mix into the carbs. When the choke is let off I can rev it a few times then it dies right out unless I hit it with the choke or pre-mix again.I rigged up a gas can on a step ladder and ran a line right to the carb and its pumping fuel like crazy out the return line.I even replaced the pump components...no change.I tried setting the pop off 4 times..40,35,30 and 25..no change.I removed all the jets and squirted WD-40 through all the ports...all clear.Apparently the prob is between the pump and the carb throats but I am out of ideas

 

[Bills86e]

Ladder? If you had a short piece of fuel line in a small glass of gas, you should see it "drink" draw the gas out, pump it thru and out the return. The difference between the Mag & PTO carbs is Mag has the fuel pulse pump (did you clear the line and pulse nipple?) and the PTO has a restrictor at the fuel exit to keep fuel pressure regulated equally in both fuel bowls. Could you have confused the Hi & lo adjustment screws? In actuality, the LSA can be turned out untill you see fuel dripping from the venturi hole, then back in for low speed richness.

I know you have worked hard on this, some times something gets overlooked, like
the fuel lines on wrong nipples. I try to use info from this forum site, I'm just starting my coffee.

Hope you discover a error, and all works to get you rideing again! Bills86e

 

[seadooya]

you mentioned about getting this "717" motor, did you pressure test it?

 

[adamzpop]

I am 99% sure the fuel lines are connected correctly and the high and low speed adjusters are set right.I have not pressure tested the engine and am not really sure how to go about it but guess that might be my next step.

Thanks