91 EZGO Gas hesitant starting

[Jednlulu113]

Great forum. I've learned a lot about small engines and the mechanics of various "toys" from these threads.
So, I have a 1991 EZGO Marathon Utility cart (venture with Jacobsen). My kids and I were pulling a small trailer whilst picking up rocks in the yard. All the sudden, while attemping to take off, she started spitting and sputtering and backfiring through the carb. I immediately suspected that the cam lobes were worn down because when I rebuilt the motor last year (sleeves were in service limit i.d. so rings were replaced and rockers where really worn down). I never even looked at the cam closely during the rebuild so, hence my assumption due to the condition of the rockers (which by the way did get replaced).
Anyway, I tore the top end off and the cam actually measures out well within the service limit (lobes). The only slight concern is that the free end (opposite of timing gear) was right at the low end of the service limit. So, I assume since rockers are new, that stack up of tolerances together should be ok.
So I move to the valves. Intake valves check out great, nice chamfers, mating all ok. Exhaust valves however, whew, what a mess. Couldn't believe it had ran that long with that condition. So, I replaced the valves (had seats ground by a local machine shop). Did the test with pouring fuel into the exhaust port...checks out great. Did same for Intake side...check, all good.
Got things all back together, new timing belt, new valve seals, new gaskets and such and she still spits and sputters upon attempting take off. She'll do this for about 5~8" and then finally fire and get moving. Once moving, all is ok and she runs good. It's just that initial take off now that's troublesome. From a cold start it takes more like 15~20" to get going, improving to 5~8" when warm.
I did check the vacuum line to the fuel pump and she's nice and tight at both ends. No improvement.

Any advice out there on what I should have a look at next?
Thanks for any insight / opinions / advice.
Jed

[Jednlulu113]

Hmm...shall I try the valve adjustment with a hot engine then? I've always done it cold but, the backfiring and hissing out the carb is part of my problem as well.
I checked thread after thread of detail and just now, today, I noticed the very helpful tech thread at the very top of the forum!
I'll try later this evening (after work :0) and report back on results. Fingers crossed!

[popatop]

Hi Jednlulu113 that is what I would do readjust the valves mine are real pickie.

[Jednlulu113]

Ok, so tonight, my son and I (he's 7-1/2...he just reminded me of the 1/2) worked on the ol girl. Got her fired up (of course with her hesitation) and road around the farm and got her warmed up. We zipped the valve cover off and proceeded to adjust the valves as per the instructions provided without the gap guages. Rotated the cam by means of the clutch so that each rocker was precisely opposite the lobes and made the adjustment. Rotated the adjustment screw with the handy dandy homemade tool with square bit screw so that it just made contact with the top of the valve shaft, backed each off 1/4 turn and locked'em down. It seemed that I had to thread each screw in quite a bit before making contact so, my assumption is that yes, indeedy, when warm the rocker shaft "pulls away" from the cam shaft just as described in other posts.
Put her back together and.....no change, she's still just as hesitant as before, backfiring and spitting fuel out through the front of the carb (I'd removed the air filter so I could look more closely).

So, considering that one end of the cam shaft is just at lower service limit, I decided that maybe I'd try and leave the two rockers most proximal to that end of the cam just a smidge closer to the lobes. Performed above procedure once again (to the two rockers most distal from the timing gear), adjusting about 1/8 a turn back away from the valve shaft instead of the noted 1/4 turn, put her back together, tried her again and....no change...maybe even sputtered moreso than previous adjustment. Mind you I've gotten this down to being torn down and back together in less than 4 minutes so, I don't think it's cooling off too much to throw things out.

So, after adjusting those two rockers back to where they "should" be (1/4 turn away from valve shaft) and putting her back together I still have a sputtering, burping, spitting machine. I proceeded to change the fuel filter (just as a grasping at straws effort) and ...still the same friggin trouble.

On another note, I'd found the thread that describes how to adjust top end speed, made some slight adjustment and she does move a little better. Greased up all the zerts, topped off the transaxle fluid (as if somewhere in my little mind I thought maybe, just maybe this heavy petting would convince her to run better) and aired up one tire that appeared low but....no change.

Any takers? Should I assume that because the end of the cam is at the low end of the service limit it should be changed (the cam)? (BTW, when I say the end, I'm talking about the end that "rides" in the Head and free spins...end closest to the cover that secures the cam and rocker rod in place.) Is there any other "thing" that would create the burping effect (backfiring)? I did replace the timing belt and the "pointers" both line up so it can't be that....and I'd replaced the "black box that makes the spark" so spark should be ok....I'm tired and can't remember what that darn thing is called....oh yeah, ignitor. I'm at a loss and ready to shoot the neighbor's cat. (Just kidding about that, that wouldn't be very nice now would it). Point is, this is making me crazy!
I've tried to think of any changepoints but don't recall that we really mistreated her at all...we were pulling a trailer (lightly loaded mind you) with field rocks loaded up when this all began.....

Any help is SURELY appreciated!

Jed

[Jednlulu113]

I'd taken a video of this but I see now that you can't attach a video directly to the blog...poo

[multifasited]

First thing I would do is check the clutch ,she may need greased and not allowing to goe to lowest possible gear ratio ,Been there done that got the tee shirt lost the hat ,remove belt grease zerk on top make sure retracks completely felt like a fool when that was all it was causing exactly the same problem ,went thru all the same proceedures .

I hope thats all it is !
Multifasited

[shadowman]

have you checked the crank seals yet? if not check them just spray with carb cleaner while running and if rpm,s change you have a seal going bad................i would also loosen the exhaust at engine and seperate about an inch an drive it see if that changes anything........................

[Jednlulu113]

Multi, I appreciate your advice, however, during the hesitation, engine won't properly "fire" to get up to enough rpm's to engage the clutch...and it's rough...really don't think it's the clutch.

Shadowman, is this diagnosis appropriate for 4 cycle? I sure hope it isn't this....especially since I just rebuild the entire motor last year, all new seals and all. There's no weeping at any seals either...If appropriate for 4 cycle, I'll give it a try but I'm reluctant.
THanks for the tips guys!

[Jednlulu113]

Shadowman, I understand now that this mehod of diagnosing can be performed on a variety of gas engines, not just 2 cycle. I apologize if I sounded like a moron! I will certainly give it a try and try backing off the muffler too. Thanks again.

[scottyb]

Have you checked to make sure you are getting good spark all the time?

Spitting gas out of the carb requires an open intake valve while under compression.