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Dampers popping out of the dashpots [w/ pictures]

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100DashSix

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I know that the force of a backfire through a carb can cause part of the damper to break through the plastic cap, but I've never heard of the entire damper sticking out (cap intact), as if it were unscrewed. I've been having trouble tuning the two HIF-4s and, sometimes, there's a backfire (not from the exhaust, from the carb) and then a lot of fluttering on accleration..lo an behold, one or both of the dampers have somehow popped up neatly, as if they were never screwed in. I've tightened them very snugly, I'm sure it's not this.

Is it worn plastic on the cap of the damper? (Oh please, I hope so) Or something more serious?

As for the backfiring, the mixture is right, the carbs are synced, and acceleration feels normal up to a point, then the car hesitates and sometimes backfires.

Edit: I'm using 10WT oil in the dampers, for the cold weather in PA.

Pictures of the dampers
 
Re: Dampers popping out of the dashpots

Without seeing it, it will be hard to answer that question...pull the damper & take a look...if you have to, remove the dashpot & look inside it.
 
Re: Dampers popping out of the dashpots

Both dampers and dashpots look good. Before trying to tune the car I removed both dashpots and pistons and cleaned them up, hoping that dirt could've been causing piston problems.

Here are some pictures.
 
Re: Dampers popping out of the dashpots

[ QUOTE ]
but I've never heard of the entire damper sticking out (cap intact), as if it were unscrewed. I've been having trouble tuning the two HIF-4s and, sometimes, there's a backfire (not from the exhaust, from the carb) and then a lot of fluttering on accleration..lo an behold, one or both of the dampers have somehow popped up neatly, as if they were never screwed in. I've tightened them very snugly, I'm sure it's not this.

Is it worn plastic on the cap of the damper? (Oh please, I hope so) Or something more serious?

As for the backfiring, the mixture is right, the carbs are synced, and acceleration feels normal up to a point, then the car hesitates and sometimes backfires.

Edit: I'm using 10WT oil in the dampers, for the cold weather in PA.

[/ QUOTE ]
Hi Dan,
I can think of a couple of possibilities. The backfire is caused by the mixture being slightly too lean during acceleration. This would normally be caused by the dampers not restricting the piston rise enough.

Maybe the 10wt oil doesn't restrict the piston rise enough. The normally recomended oil is 20 wt which would make the mixture richer during piston lift. Cold weather would increase the need for more damping.

I think there are two different jet needles that are normally used. The AAU & the ABD. Of the two, the ABD is slightly richer in the midrange. This could help the problem.

Likely the threads are worn on the damper caps which allows them to pop out.

I would try replacing the caps & using 20 wt oil. If this doesn't cure the problem, check the needle markings for type & put in the ABD needles if they are not already in there.

Other causes of pop back could be point gap too close or ignition timing off. Also too low float levels.

One check would be to pull the chokes to richen the mixture when the pop back happens.

Good luck,
D
 
Re: Dampers popping out of the dashpots

My dampers would push out of my HS4 carbs on my '78. I removed the rubber washer and replaced with a little thinner one...solved the problem.

FWIW...may *not* be your problem.
 
Re: Dampers popping out of the dashpots

Dave, that sounds like excellent advice, as usual. (You've helped me with questions on my other SUs.) Before I tried the 10wt oil I used what I had for my other car: 30wt. The 10 was definitely better than the 30, but I'll try 20 next. I'll also see what needles I'm using.

I'll get some new dampers and maybe ABD needles, if I'm not using them. If none of this stops the backfire, I'll check the float levels...if all of that fails, I'll have to carefully drive it to a mechanic, I fear, as I don't have the required tools to check timing here (though I suppose I could get a gap-checking tool, and check the points).

Thanks Dave
 
Re: Dampers popping out of the dashpots

I've always used auto transmission fluid...when I bought my '79 new, that's what the service manager at the MG dealership recommended.
 
Re: Dampers popping out of the dashpots

The race crowd indeed uses 10w oil or ATF in the dampers as they feel it quickens acceleration somewhat. I've always used Castrol 20w50 with no ill effects.
 
Re: Dampers popping out of the dashpots

I would run straight 30W in the dampers in PA in the middle of winter with no problems. There were a batch of "counterfeit" dampers produced and sold thru the "usual suspects" back in the '80's... I'd say get new dampers, use ATF, and the thin fibre washers and the prob will become a memory.

Just my opinion, mind you.
 
Re: Dampers popping out of the dashpots

I run whatever motor oil I'm using. Usually 20w50.
 
Re: Dampers popping out of the dashpots

ditto... I use whatever motor oil I have on hand in me ZS dashpot
 
Re: Dampers popping out of the dashpots

So, it sounds like it's not as simple as the type of oil in my dashpots. Since the car feels like it's stumbling as the RPMs reach a certain point, it must mean the mixture tends to become more lean there. This either points to the tapering of the needles or the level of the fuel in the floats on the HIF-4s, correct?

Or could the carbs be out of sync during high revs, with one drawing more in than the other? Also, could this be caused by a serious leak, perhaps worn bushings in the throttle shaft? Maybe the draw happens to get enough to suck in false air at a high RPM, suddenly leaning the mixture and causing sputtering and carb backfires. Sound plausible?
 
Re: Dampers popping out of the dashpots

I had the same problem on our MGB several years ago. After trying every fix I could think of, I finally ordered new dampers - problem solved, the threads ont he caps were apparently just worn too far to hold sufficiently. Good luck
 
Re: Dampers popping out of the dashpots

Dan, My back carb would pop out the dashpot with no effort at all. The car would be running great and all of a sudden it would start to act crazy. Opened the hood and the back dash pot would be sticking out. I did what Rick did and put in a thinner gasket. It worked for now but I think I'm going to get a pair of new ones. The plastic threads are worn and I don't need this to happen on the road! PJ /ubbthreads/images/graemlins/driving.gif /ubbthreads/images/graemlins/thumbsup.gif
 
Re: Dampers popping out of the dashpots

Looking at those photos makes me think all that's happening is they're backing themselves off the threads....I think th bottom thread on yours is a bit worn & there's nothing to hold them tight....so, they vibrate loose
 
Re: Dampers popping out of the dashpots

Yepper... threads look so worn they're tapered. Replace 'em.
 
Re: Dampers popping out of the dashpots

Easy fix, duct tape till you get new ones.
 
Re: Dampers popping out of the dashpots

ya..like tony said.....
also use 20w50....its no colder in
virginia than it is in arkansas and
my car runs good with 20.....
ur car also might sputter as its running
out of gas! ; ) just checkin
 
Re: Dampers popping out of the dashpots

Hmm, looks like black stuff, plastic, inside the threads of the dash pots. Duct tape em in, do not block vent hole, and order a couple of new ones.
 
Re: Dampers popping out of the dashpots

And wait 'til you've got the new ones in place before you start "looking for trouble". The lean pop cold can easily be sloppy shafts, use more choke when cold and see if that changes. If the carbs are sync'd correctly at the "bottom" they are generally good right thru the range. You can usually tell if the shafts are suckin' air easily at idle: shoot some aerosol "something" (WD-40, carb cleaner, starter fluid, etc.) on the shaft ends and note if there's a change in RPM. If so, they're "leaking". Really, a simple "wiggle test" can tell you a lot too. If you can move the shaft any discernable amount tangent to itself in the body, you're likely to have bypass. It'd have to be a lot for it to affect the higher RPM mix tho. Most noticeable at lower (idle) RPM.

Hope there's something there you can use.
 
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