Pulse hose

[rocketman17joe]

IVE BEEN HAVING TBL WITH MY 400 JLO.IT RUNS GREAT UN TILL 15 MIN INTO MY FUN THEN BOGGS AND DIES . I TRYED ADJ CARB,CK FOR AIR LEAKS VIA CARB CLEANER,I TRYED ADDING A SMALL ELECTRIC FUEL PUMP EVEN THOU IT ONLY HAS 2PSI IT RUNS WORSE.NOW MY THOUGHT,IM GOING BACK TO THE PULSE PUMP THE ONLY THING I CAN THINK OF IS THE OLD PULSE LINE WAS A HARD PLASTIC TYPE I REPLACED WITH STD FUEL LINE.IS THIS WRONG ? IF NOT IM READY TO RUN IT OVER WITH MY TRUCK.......

HELP

[hydromike]

Hey Joe,

If it runs great for 15 minutes and then dies, it sounds like a fuel delivery problem. I haven't gone back in your posts to see what sort of machine you have, but I'm suspecting it's an Attex or a Max. The fuel lines in these machines become brittle, and tend to collapse and/or swell shut over time. I would start by running a new fuel line all the way from the INSIDE of the fuel tank, to the fuel pump. The pulse pump doesn't sound like it's the issue to me, if it's delivering fuel for some amount of time. Standard fuel line will work OK for a pulse line, as long as it's not REALLY gummy so that it collapses. Again, if it runs well for 15 minutes, it sounds almost like the fuel pump is working too hard (against a plugged/collapsed line?) to keep up with what the engine needs.

If it's sputtering and not fouling plugs, it doesn't sound like it's a coil issue, where the coil works intermittently until it gets hot, and then konks out when resistance gets too high. This genuinely sounds like fuel delivery.

*New fuel line
*New fuel filter (don't forget to clean the fuel pickup IN the tank!)
*Check all your fittings and make sure they're clamped on at all connections to the fuel pump, carb, crankcase, fuel tank, etc.
*Clean out float bowl well.
*Check your fuel shut-off valve (if so equipped) to make sure it's not blocked at all.

Let us know how you make out. Don't run it over with your truck.

~M

EDIT:: After reading through several old posts, I see that you've cleaned out your tank and run new lines, etc. on your 400 Chief, and have been through a couple different carburetors. The 34 Mikuni is about as big as I'd go on a 400. Do you know what main and pilot jets you're running on it? It sounds to me that the fuel pump still can't keep up with your fuel needs for whatever reason. If you haven't gone through and put new crankshaft seals in, that may be the way to go. They're not incredibly hard to do, but it's time consuming.

[golpher76]

I have read a lot about those pulse powered fuel pumps. I recommend getting some heavier line for it other than standard fuel line as the standard line tends to collapse and will cause issues as it warms up from engine heat(which might be why it runs fine for 15 minutes and then dies). Napa and advance auto both sell 1/4" nylon reinforced rubber fuel line by the foot that's what I replaced all my line with including the pulse line, they also sell the hose clamps for it in 10 packs for around 4 dollars behind the counter so don't buy the 2 packs on teh shelf for 4-5 dollars it's just a ripoff. Also be aware that if your pulse line is over 15" long it causes a low pulse pressure condition, it is recommended that it be less than 12" if possible so I am running mine at 9" just to be safe.

[rocketman17joe]

I did replace lines and the pulse line is aprox 1 1/2 ft long.i do believe it a fuel prob but i tryed the carb cleaner trick to see if the seals were leaking when hot and the engine didnt change rpm's when sprayed.i can tell you when it does die i pull the choke to restart.also it does have a new carb

[rocketman17joe]

Two questions.what would the jets have to do with this problem? And i did spray the seals when the tbl starts and it dosnt change rpm.and one more thing what is involved with replacing the seals and di i have to remove th whole bottom or the engine????

[Jeff t-boss]

Is your fuel tank vented? And if so, is the vent/breather clean and free of any restrictions?

[racerone3]

I did replace lines and the pulse line is aprox 1 1/2 ft long.i do believe it a fuel prob but i tryed the carb cleaner trick to see if the seals were leaking when hot and the engine didnt change rpm's when sprayed.i can tell you when it does die i pull the choke to restart.also it does have a new carb

just a thought, a lot of carb cleaners these days are non flamable. it's getting really hard to find brake clean that will burn. i never used to keep ether around, just grab most any aresol can off the shelf, but these days ether is one of the only things in a can that will go boom! you might want to repeat the test with ether or propane (small torch with the gas on, not lit. aimed behind the clutch and again on the recoil side)

[hydromike]

Your pulse line should be as short as possible. 1.5' seems aweful long. Keep the fuel pump as close to the engine as possible, just as long as it doesn't get hot. Mount it relatively low; they push fairly well compared to how they pull from the tank. They should really be gravity fed, and pulse-pushed from the pump to the carburetor.

The jets may have nothing to do with your problem, but simply throwing a 34mm carburetor on an engine that originally came with someting along the lines of a 28mm carburetor is a big step. If it's a new carburetor, the 34mm is likely generically jetted for a better-breathing and/or larger displacement engine. Just another variable in the equation of an efficiently running engine, really....

~m

::EDIT::

you might want to repeat the test with ether or propane

True 'dat. Get some ether and douse it.

[LarryW]

I didnt really read all the post here so sorry if I am restating what someone else might have stated but the line in the tank that goes from the fitting to the pick up filter should be checked maybe? I have seen old rotten lines cracking and such inside. Also for the pulse pump if the line is short you can run a spring in it to keep it from collapsing. Just a couple quick thoughts I had. Hope you figure it out!