Trying to figure out why my car is stuttering sometimes under acceleration, with a problem starting while hot too. I did the valve clearances already (650cc with a .008 and .010 clearances for intake and exhaust, respectively), it's a new carburetor however it is a cheap Chinese build so it could still be a problem. I also installed a 123 Ignition on the vehicle and set static timing, however I'm not sure about the dynamic as I dont have the marks for the 28* btdc, however it seems okay and I get good strong spark at the plugs. But it looks like under acceleration I'm getting air bubbles into the fuel filter from the pump. It may just be vibrations causing it but anyone have an opinion on a cause? I was told a fuel leak somewhere may also cause the hard start while hot, and I think it would potentially cause stuttering if air is getting in, I just cant seem to locate any fuel leaks. All I have are a few minor oil leaks (which I will eventually take care of). I have attached a video for example (in this the choke is pulled all the way to produce a high idle and helps demonstrate the stuttering issue as you can see I open the throttle and accelerate is delayed/stutters.

Video here:
https://app.box.com/s/xuk6kgzo6i9t7u0449re328gds7etvcg

It is not uncommon for air to show in a filter in that position however having watched the video I am always disturbed when I see a plastic filter fitted between the fuel pump and carb as it is so dangerous. If the fan belt or cooling fan fail and the engine continues to run you could be minutes away from the car going up in smoke and the overheating engine bay having melted the plastic filter.
The reports on the reproduction carbs have not been good with one supplier saying so many have been returned that you are better off with a refurbished original Weber carb. I spoke to a guy last week who had one and the fuel enrichment device (choke) did not connect with anything inside the carb so did nothing

To be honest that doesn’t look right. As Toshi says it is common to see bubbles in the filter but I have never seen one that bubbles up like that when it is rev’d, which sort of suggests there is an air leak somewhere. The bubbles are normally fairly constant at tickover and just tend to move around a bit when rev’d but yours seems to froth up.

I used to be an advocate of online filters but as I have posted on other threads they really don’t achieve much. With modern fuels they are even thought to hamper fuel flow, so I have ditched them now and run without one. If anyone is proof of this it’s Peter he doesn’t run with one and look at the faultless miles he runs.

That much air frothing around in the filter looks strange---although I appreciate that some of the 'frothing' will be engine induced vibration. I would endorse my colleagues suggestions that you do NOT have a fuel filter between the pump and the carb. There are already 3 filters in the system, tank pick-up, pump and carb, and due to the high rate of useage at most petrol stations these days, there VERY few instances of duff fuel. When I was a lad, fuel useage was much lower and 'rubbish' and water coming through with the fuel was much more common.
As to you running problem--have you set the timing with a timing-light, or by ear? To get the 28deg mark, put a small dab of paint (tipex?)on the filer pulley about 14mm BEFORE the TDC mark. This will come back to the TDC mark when you are at 28deg before TDC. (if I have got this the wrong way round, feel free folks to correct me!)
I would also check that you have no air leaks around the base of the carb; when the engine is running, spray some carb cleaner around the bakelite spacer--if the engine revs increase, you have an air leak---remove the carb, ensure that the base of the car AND the spacer are all absolutely flat and refit with new gaskets.
Finally, the Chines made carbs are, to a greater or lesser extent, a waste of money. Parts are not cast correctly and/or parts are not even connected!

SpyderJava said:

Trying to figure out why my car is stuttering sometimes under acceleration, with a problem starting while hot too. I did the valve clearances already (650cc with a .008 and .010 clearances for intake and exhaust, respectively), it's a new carburetor however it is a cheap Chinese build so it could still be a problem. I also installed a 123 Ignition on the vehicle and set static timing, however I'm not sure about the dynamic as I dont have the marks for the 28* btdc, however it seems okay and I get good strong spark at the plugs. But it looks like under acceleration I'm getting air bubbles into the fuel filter from the pump. It may just be vibrations causing it but anyone have an opinion on a cause? I was told a fuel leak somewhere may also cause the hard start while hot, and I think it would potentially cause stuttering if air is getting in, I just cant seem to locate any fuel leaks. All I have are a few minor oil leaks (which I will eventually take care of). I have attached a video for example (in this the choke is pulled all the way to produce a high idle and helps demonstrate the stuttering issue as you can see I open the throttle and accelerate is delayed/stutters.

Video here:
https://app.box.com/s/xuk6kgzo6i9t7u0449re328gds7etvcg

Click to expand...

Hi Spyder, I concur with previous posts - move your filter away from it's present position, there's a world of pain awaiting you with it there!!!!
I also agree about the frothing of the fuel, to me it's all vibration induced, and don't worry about the fuel level in the filter - I run an electric pump with a similar in-line filter in the front and mine never fills completely. Once you are happy with your timing and valves turn your attention to the carb !!! try a replacement if you can borrow one with the same settings

Ian.

How do you identify one of these Chinese made carbs? How are they badged? Are they badge Weber?

I know the later polish carbs, which I believe were made under license from Weber, had some sort of sailing ship badge on them.

Mine has no badging on it at all, it's been grounded off of it. The only Mark's on it are ones identifying the 28IMB. I also know that when I bought it it was shipped out of China by the tracking information.

I'll replace the fuel filter, I in fact only recently installed it when I had replaced the carb, before that it had been running with no filter.

As for the timing I used a timing light but had no reference to identify the 28 btdc. When marking on the pulley is it 14 mm clockwise or counter clockwise from the timing mark that is already on the pulley?

Thank you everyone for the quick responses.

Vitesse said:

How do you identify one of these Chinese made carbs? How are they badged? Are they badge Weber?
.

Click to expand...

I was checking out all of the new and used 28IMB carbs on ebay last week trying to help a guy get the right one for a very late engine. Original carbs were made first in Italy then the bulk of production in Poland. I believe that some recent repros were made in Spain possibly under some sort of licence. These can be recognised by not having the internal mesh filter by the fuel inlet hence no brass hexagon cap to seal it in which I guess was a cost cutting exercise. However looking at the carbs one of the new ones stood out as it looked odd to me. Right sort of shape but the shiny castings looked rough and poorly finished. There seemed to be no identifying markings when you zoomed in. Checking the item location it said Hong Kong so I imagine that these are just fake Weber carbs.

F D Ricambi in The Netherlands sell what appears to be what Toshi describes as the Chinese one, see picture below. But they also do some decent rebuilds of Polish made carbs for the 126 which are pretty reasonably priced. I know as I bought one for for my late 650 distributor less engine.

Vitesse said:

F D Ricambi in The Netherlands sell what appears to be what Toshi describes as the Chinese one, see picture below. But they also do some decent rebuilds of Polish made carbs for the 126 which are pretty reasonably priced. I know as I bought one for for my late 650 distributor less engine.

Click to expand...

No you misread that. The one shown there is what I believe is the Spanish one. I have never seen one in the flesh but there are loads for sale between £160 & £260 from what I remember. The tell tale sign is the missing big brass cap.

living where you are (in Italy) I am amazed that you can't find a good, used 28IMB carb (a genuine one) for your Fiat. Look at scrap-yards (they must have such a place in Italy!) and get hold of a carb off a LATE 126. You can easily tell the difference between an early (594cc) 126 and a later (652cc)126---look at the wheels. If the wheel bolt pattern is the same as a normal 500 (190mm pcd) it is an early 126 (Mk 1)---if the wheel bolts are nearer the centre of the wheel (normal sort of pattern--98mm pcd) then it is a 652cc Mk2 126. The carb. will fit straight on, but make sure that the carb's base-flange is flat and that the bakelite spacer is also flat on both surfaces. When you have done this--get rid of the 'Chinese' carb.

the hobbler said:

To get the 28deg mark, put a small dab of paint (tipex?)on the filer pulley about 14mm BEFORE the TDC mark. This will come back to the TDC mark when you are at 28deg before TDC. (if I have got this the wrong way round, feel free folks to correct me!)

Click to expand...

Well you did say......

If I'm reading you correctly I think that would be at around 342 degrees before or 18 after TDC.

If you take the helpful calculations already done by Chris Bambino:

https://www.fiatforum.com/500-classic/226412-help-setting-ignition-timing-fiat-500-f.html?p=2402226

....you will find that because the engine turns clockwise as viewed from the rear of the car, to find the location to make a timing-mark for 28 degrees before TDC which is suitable for a strobe, a Tippex mark can be painted on the pulley 36.68mm in a clockwise direction from the TDC casting-mark on the pulley.

I've said many times before, many people will not have this set up properly either through a lack of understanding and/or lack of the stroboscope to verify and adjust, or because their distributor is worn and/or badly adjusted and unable to achieve a stable level of advance. With the 123 distributor you should already be in this ballpark because of its inbuilt accuracy and electronic timing and advance. As an aside I suggest this is one of the contributory reasons as to why users are so pleased with the improvements the 123 brings to the running of their engine.

Toshi 975 said:

No you misread that. The one shown there is what I believe is the Spanish one. I have never seen one in the flesh but there are loads for sale between £160 & £260 from what I remember. The tell tale sign is the missing big brass cap.

Click to expand...

Yes you’re right I did misread it didn’t I Dave :doh:

I will run my engine tomorrow morning,check the timing with a 'strobe' and report back---if I have got it "arse about face" I will say so, and describe how to do it properly---watch this space, I could be walking around with a large egg on my face!

I had one of these made a while ago. Very handy for timing the engine.

Chris

As promised, I have run my engine this morning, with the timing light. I made a (tipex) mark on the crank-shaft pulley, just to the right of the first oil-filter securing bolt, which is just to the right of the TDC timing mark on the cover. This is when looking at the engine from the rear---the crank will be turning CLOCKWISE. When the engine is running at idle, the 10deg mark on the cover will (when using the timing light) align with the mark on the crank-case. As the engine is revved, the timing mark will appear to move ANTI-CLOCKWISE. It isn't, it is just the timing light is showing where the ignition point is in comparison to where the indicator is on the crank-case. The temporary mark for 28 deg BTDC will (when the engine is revved) also seem to move backwards, and will, if all is set up correctly align itself with the timing mark on the crank-case.
I will concede that this is very simplistic, but it is an easy way to show it.

the hobbler said:

As promised, I have run my engine this morning, with the timing light. I made a (tipex) mark on the crank-shaft pulley, just to the right of the first oil-filter securing bolt, which is just to the right of the TDC timing mark on the cover. This is when looking at the engine from the rear---the crank will be turning CLOCKWISE. When the engine is running at idle, the 10deg mark on the cover will (when using the timing light) align with the mark on the crank-case. As the engine is revved, the timing mark will appear to move ANTI-CLOCKWISE. It isn't, it is just the timing light is showing where the ignition point is in comparison to where the indicator is on the crank-case. The temporary mark for 28 deg BTDC will (when the engine is revved) also seem to move backwards, and will, if all is set up correctly align itself with the timing mark on the crank-case.
I will concede that this is very simplistic, but it is an easy way to show it.

Click to expand...

I agree Tom; that is exactly what happens. But as you say now, the marks for 10 and 28 degrees BTDC must be made to the right and then further to the right of the TDC raised mark on the pulley.

Okay. Moved the fuel filter in line by the fuel tank, and it was running good for the most part. Now, she sat for about a week or two and when I went to start her up today she seems to run a bit rough and on top of that there seems to be a decent amount of backfire. Any ideas as to a possible problem? I doubt it's a timing issue being as it is a 123 ignition system and new plugs and wires and the timing was good. I also recently checked the clearances a few days before parking her and everything was good. Maybe a carb issue? I'm going to take her to my work and have a look at her better, but any ideas from you guys is always appreciated. Thanks.

Video of misfire:
https://app.box.com/s/eqb7l3ludx7nkvl3zcv4ztspxxnvm71o

Fuel pump?

Can you get a clear fuel line from the pump to the carb, will indicate if this is an issue or not.


Also. get a multimeter on the plugs and wires to ensure you have no resistance. Just because they're new, does not mean they are good!

R

I will see if I can find a clear fuel line to put in to see if that's an issue. I will do a resistance test on the wires when I get to work Wednesday. Thanks for the suggestions.