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Hgpilot

XF 4.1 popping!

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Hi, I'm a new member to this forum. I have an XY Ute with an XF 4.1 carby engine in it. It's been sitting in the shed for about 10 years so I have decided to do something with it. 

It would hardly run at all with constant misfires and backfires about 2 weeks ago. I since found the distributor just floating around with locking screw undone. Set timing to 6 deg btdc and replaced leads and plugs. It runs alot better now and actually idles. The problem though is that it makes an awful POP sound every 3 seconds or so and the engine shakes and will even stop if in gear. I suspected maybe blow past one of the exhaust valves but I checked compression and all cylinders are between 120 and 150 psi. Also the POP can't be heard in the exhaust, only in the engine, I think from the carb. The popping gets less severe as the engine heats up and stops completely when revs are high. It does pop every time the throttle is suddenly opened. Any help would be appreciated. Thanks! 

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have you checked where the timing is? might be retarded, set it around 15deg advance (to compensate for worn timing chain) and if it pings when driving can retard it(or add 95 fuel.. )
 

otherwise,  could be just a carby with dry as chips diaphrams. or an air leak..
bedtime for Me now, i'll check your reply in the morning

 

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Hi, yes I set the timing at 6 deg btdc but I originally set it at 10 deg btdc and changed it thinking I may have had preignition. I will try and advance it to about 15 tomorrow afternoon. You are probably onto something with the diaphrams in the carby 🤔.  This engine has not ran right for at least the 15 years I have owned it. I have read some forums suggesting maybe to much fuel flooding in on idle? I would appreciate your thoughts. Thanks! 

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Thanks! Had a read through and watched the vids. Little bit different from my issue I think. In the video, the engine seemed to be delayed and not very responsive. Mine is very responsive to the throttle but just makes an awful POP out the carb when I push it or at idle. 

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Vacuum leak.

 

try spraying a little Ether (Aerostart, Start Ya Bastard) around the carby base, inlet manifold etc...while running... dont worry too much about what the harmonic balancer says, just twist the dizzy to get it to idle and rev, then check the timing marks. 

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Yeah no worries I havnt tried that yet. I will have a look around with the aerostart this arvo. Wouldn't surprise me if there is a vacuum leak as I have had to repair 4 different split fuel lines. 

When you say just twist the dizzy to get the idle, do you mean until it idles at its highest or just till it sounds about right? I have the idle screw in a long way atm with it at 6 deg. Should I wind it back out and just advance it till it sounds good? Thanks! 

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Yeah, mate till it sounds ok. Should rev free, should stop dead when you turn the key off, and not run on (diesel knock), and start easy even when hot. Try timing at 8, then 10 deg, then 12, if you like. 

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Thanks Bear! I have just finished playing around with it again. Seems to run well at 10 deg,  so I have left it at that for the moment. I just replaced my thermostat housing and found a little vacuum line off but still popping. I tried spraying some aero around the intake but didn't notice any change in sound. The weird this is though, I sprayed it in the carby and only noticed a slight change in noise anyway.

Forgive me for not being all that knowledgeable with these engines (its why im here) but I traced out some vacuum lines and noticed that one goes to the transmission. With the transmission, it has always struggled to shift up. You have to rev the guts out of it and maybe it will shift. Isn't there some sort of vacuum modulator or something on a 3 speed C4 trans? (The trans is out of an XC Fairmont that I threw in about 10 years ago with my father).

Also, when I pull a vacuum line off it seems to make not difference and when I spit on my finger and put it over a vacuum line, I can't feel any vacuum at all. The vac advance seems to be working with the timing though. I'm wondering if there is just a vacuum line dangling next to the trany now🤔 and I just had a shower 😡

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the vacuum modulator on the trans often has that hose perished from age or oil contamination.. i cant remember what affect it has, but it needs it

 

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4 hours ago, deankdx said:

the vacuum modulator on the trans often has that hose perished from age or oil contamination.. i cant remember what affect it has, but it needs it

 

 

Yep, needs a good hose. Modulator can be replaced, think any Trans shop should have one. or even Evilbay.  Check fluid level, too, too low and will need more revs to clunk into gear.

Is fluid nice, bright, pink stuff.?   Or does it look brown and stinks like burnt varnish?  

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Yeah it has bright red fluid and is probably to full if anything. Not sure if it smells or not. I will check this arvo! Along with the vacuum hose. Thanks! 

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9 minutes ago, Hgpilot said:

Yeah it has bright red fluid and is probably to full if anything. Not sure if it smells or not. I will check this arvo! Along with the vacuum hose. Thanks! 

too full isn't good for them.. 
make sure it's correct level

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Ok so I have an update. Jumped under the car this arvo and sure enough, I must not have connected the vacuum line to the trany all those years ago. So then, with full confidence, I turned the key on and sure enough POP POP POP😡. The trany shifts up no problem now though!. That's one problem sorted!  

The idle was alot lower after connecting the hose though. I have wound the idle near all the way in and it's still a bit low. The idle also keeps changing day to day, even minute by minute!. I will get the idle good and then 10 mins later it's way high so I wind it down and then 10 mins later it stalls. I must still have a vacuum leak somewhere? Will I need to try timing again after fixing some of these vacuum leaks? 

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there are temperature related vacuum ports for the emissions, no idea what they do or which it would be. 
but it could be that one is opening when warm and not hooked up or split hose making the vaccum leak

 

 

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Interesting 🤔. It does get.much better as the car warms up. I had it not popping at all when warm today but soon as I put the engine under some load in gear and take it for a spin, it starts popping again. And still pops when cold. I have looked up a few vacuum diagrams but they are all different to mine in one way or another. Thanks for info! 

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if you had a video on it, it might explain it better.
i'm wondering if its just a flat spot due to accelerator pump not working(diaphram) or some other simple thing

 

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