Technical Backfiring Issue

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Technical Backfiring Issue

Joined
Sep 9, 2014
Messages
266
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Location
New York
All... Having a backfiring issue when letting off gas before shifting. Also when downshifting and coming to a stop, it seems to want to stall. I have to give it throttle. This happens even if I turn the idle screw in so it idles higher and adjust fuel mixture. What gives?? Is it timing (I have a 123), fuel mixture or something going on internally? It's driving me crazy that I can't sort this out.
BTW...I installed a new carb as I thought that was the issue.
 
If your engine is standard, this might (and I repeat, might) mean that the timing chain/sprockets are worn and the valve/cam timing is out of sequence. If your engine is tuned, it might just be a reflection of the valve timing/valve overlap. My engine (a tuned 650, 126 engine) does this on the over-run---sometimes the pops 'n bangs are quite loud! If the engine has high mileage on the original timing-chain/sprockets it is not unknown for the teeth on the timing sprockets to become badly worn---the valve timing can then 'jump', and you only require it to be one 'tooth' out for strange things to happen.
 
If your engine is standard, this might (and I repeat, might) mean that the timing chain/sprockets are worn and the valve/cam timing is out of sequence. If your engine is tuned, it might just be a reflection of the valve timing/valve overlap. My engine (a tuned 650, 126 engine) does this on the over-run---sometimes the pops 'n bangs are quite loud! If the engine has high mileage on the original timing-chain/sprockets it is not unknown for the teeth on the timing sprockets to become badly worn---the valve timing can then 'jump', and you only require it to be one 'tooth' out for strange things to happen.

This could be. I'm sure it's high mileage on my engine as it appears to be original. Difficult job changing the timing chain/sprockets? Didn't think of this when engine was out when we were restoring the car.
 
Totally agree with 'Toshi'----check your tappet clearances first of all; the '110' engine has a habit of them closing up. In answer to your question regarding the renewal of the timing-chain and sprockets, it is not a difficult job and can be done with the engine still in situ. You support the engine with something under the sump (preferably NOT a jack), remove the rear cross-member complete with rear engine mount and the timing-chain cover is there in front of you. The only difficult bit is undoing the crankshaft nut which should be tight. After that it is basically just taking off the 'V' belt pulley, removing the oil-filter housing (can go on in only 1 position), undoing the timing-chain cover and exposing the sprockets and chain. Again, the sprockets will be marked so that you can time the cam vis-a-vie the crank. Get the best quality timing-chain/sprocket assembly that you can. Please keep us advised as to developments.
 
Totally agree with 'Toshi'----check your tappet clearances first of all; the '110' engine has a habit of them closing up. In answer to your question regarding the renewal of the timing-chain and sprockets, it is not a difficult job and can be done with the engine still in situ. You support the engine with something under the sump (preferably NOT a jack), remove the rear cross-member complete with rear engine mount and the timing-chain cover is there in front of you. The only difficult bit is undoing the crankshaft nut which should be tight. After that it is basically just taking off the 'V' belt pulley, removing the oil-filter housing (can go on in only 1 position), undoing the timing-chain cover and exposing the sprockets and chain. Again, the sprockets will be marked so that you can time the cam vis-a-vie the crank. Get the best quality timing-chain/sprocket assembly that you can. Please keep us advised as to developments.


Or if I am not mistaken you can get a gear replacement that does away with the chain and sprockets...…...I believe 'Bleeding Knuckles' has fitted one to his ongoing build.....
 
New valves were installed when my heads were redone.


Deffo check your valve clearances then...….
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You are indeed correct---the supplier for the timing GEARS is:---"D'angelo Motori"----www dangelomotori.it They have a very good little catalogue (in English!) and can supply some very good looking gear. They are also the main agents for:--Lavazza Tecno.
 
I would check the valve clearances (tappets) before you rush into anything drastic.

I have several times and adjusted to spec clearances. But I wonder if my timing marks are truly TDC now if the chain and sprocket are worn. I guess I'm going to have to change them as it's probably a good idea anyhow. Now I just have to find the time.
 
Totally agree with 'Toshi'----check your tappet clearances first of all; the '110' engine has a habit of them closing up. In answer to your question regarding the renewal of the timing-chain and sprockets, it is not a difficult job and can be done with the engine still in situ. You support the engine with something under the sump (preferably NOT a jack), remove the rear cross-member complete with rear engine mount and the timing-chain cover is there in front of you. The only difficult bit is undoing the crankshaft nut which should be tight. After that it is basically just taking off the 'V' belt pulley, removing the oil-filter housing (can go on in only 1 position), undoing the timing-chain cover and exposing the sprockets and chain. Again, the sprockets will be marked so that you can time the cam vis-a-vie the crank. Get the best quality timing-chain/sprocket assembly that you can. Please keep us advised as to developments.

Hobbler....If I tackle this myself and change the timing chain, is it just removing and installing? Does the camshaft have to be re-timed or anything that is beyond a backyard mechanic like me?
 
I just ordered a new timing chain and sprocket. Any one else out there that has experience doing this? Is it just a simple swap and just re-time with a timing gun?
 
You will not need a timing-light as it is a purely mechanical job. The sprockets (1 on crank and 1 on camshaft) can only go on one way, and are marked on both the sprockets for timing alignment. If you buy a kit where the timing chain has the little 'wedges' on the links, these go on the OUTSIDE. For a description of the job, look on my earlier post on this subject. If you want a more detailed description, contact me direct ([email protected]) and I will try to help you out. Go through the procedure carefully and methodically and you will find it quite easy, and at the end of the day, very satisfying.
 
You will not need a timing-light as it is a purely mechanical job. The sprockets (1 on crank and 1 on camshaft) can only go on one way, and are marked on both the sprockets for timing alignment. If you buy a kit where the timing chain has the little 'wedges' on the links, these go on the OUTSIDE. For a description of the job, look on my earlier post on this subject. If you want a more detailed description, contact me direct ([email protected]) and I will try to help you out. Go through the procedure carefully and methodically and you will find it quite easy, and at the end of the day, very satisfying.
Part is in. Going to give this a try. I will report back with the outcome. Thanks for your help.
 
With the advice of Hobbler, I changed the timing belt which was fairly loose and worn. Not an easy task removing that crankshaft bolt but made 100% easier with an impact wrench which I went and purchased. But to my dismay, it still backfires. Timed with a timing light, advanced, retarded and nothing worked. Doesn't backfire all the time but it's there. The car runs OK so I may just have to live with this as I can't understand what else it could be at this point.
 
As per your other thread, if you're not getting the fuel burnt in one of the cyclinders due to ignition problem, then this could be the cause of your issue.

I suspect once you fix the ignition concern, this one may go away as well.

R
 
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