Carb issue - fuel in cylinders

kyamon · Jan 13, 2018

I am not sure if this issue is more funny or more embarrassing... I have tried to fix my carb today (a Stromberg 175 on a 6-cyl engine in a 1974 series III) because it was leaking, and I felt that I had low power from the engine. I reassembled everything (or not, maybe?) and took the car for a test drive around the block. Everything went well until I had to reverse, so for a moment the engine was idling and at that point it stalled. I was only about 100 m from home, but it was impossible to push her, so I had to call for help. Long story short - it took us quite some time to find it: the engine and exhaust were completely filled with fuel - I did not even know this was possible...

Quite obviously there is something wrong with the carb, and gasoline is pumped straight through it and into the engine. I have not yet taken it apart again, but I am wondering if anyone of you has ever seen this, and/or if it is obvious what is wrong?

Any help is appreciated!

freelance · Jan 13, 2018

Check the needle valve in the float chamber, or perhaps you have put float upside down

kyamon · Jan 13, 2018

freelance said:
Check the needle valve in the float chamber, or perhaps you have put float upside down

Thanks - I had not removed the floats, so they should be fine. However, if they for some reason are stuck in the "low" position and the gas inlet valve is always open, would that eventually push the fuel up into the engine?
What should I look out for with the needle valve? Could it remain stuck in some position?

freelance · Jan 13, 2018

Needle valve, float stuck so it just floods

kyamon · Jan 13, 2018

Got it. Will check that.

ciderman · Jan 14, 2018

be careful: fuel will have removed the cylinder wall lubrication. then, it will have thinned your sump oil and possibly made the crankcase fumes explosive......

kyamon · Jan 14, 2018

ciderman said:
be careful: fuel will have removed the cylinder wall lubrication. then, it will have thinned your sump oil and possibly made the crankcase fumes explosive......

thanks for the tip! It is time for an oil change anyway, and I was planning to squirt a bit of oil into the cylinders precisely because of that - will that do it?
Not sure what to do about the fumes... I did manage to drive it home in the end yesterday, after draining all the gas from the cylinders. But since the entire exhaust had also been filled, at some point I produced a (apparently quite impressive) afterburner. I dont mind as long as it stays behind the exhaust pipe, but I would certainly prefer this not to happen inside anything!

In the meantime I took the carb apart again and hunted for the issue. The needle valve seems fine, and even some additional cleaning did not change anything, fuel still gets pumped all the way through the carb. My impression is that somehow the leak is through the manual choke mechanism - could this be? I have no clue how to fix this.

rob1miles · Jan 14, 2018

Odds on its still the float, the pump is low pressure and the float valve can hold it back, only letting fuel through into the carb if the float chamber level drops. I'm not aware of any bypass to the float valve it would make no sense so either the valve is not holding the pump flow back or there's a broken gasket on the float bowl allowing a flow direct into the manifold. Re petrol in oil and exhaust, yes it could go with a right bang but it evaporates quickly so it should be ok by now.

kyamon · Jan 20, 2018

So... I replaced the needle valve, and at least did not flood the engine again

However, I now seem to have the opposite problem. I was driving it for a while today (relatively cold day, if that might have an effect...), and after about 30 minutes started having sudden (and complete) loss of power, to the point where the engine would stall while driving. It was an issue mostly when driving uphill but got worse and after a while persisted even when it was flat. Driving in 2nd gear at 15 kmh was OK, but anything beyond that was problematic. Usually the problem went away temporarily when I took a break and let the engine idle for a few minutes.
I have the impression that this is some sort of fuel delivery issue, does that make sense? The pump is electric and new, but the fuel lines mostly are old (dont know how old). The engine has 35000 km, and since I have the car never had as much power as I would expect - my top speed has been 85 kmh, and as soon as it goes even the slightest bit uphill I have to switch to 3rd gear, otherwise it slows down. Since this is my first land rover I have no feeling if this is normal or if something is wrong, but it certainly seems a bit weird, and after today I am thinking that maybe I have had a problem all along that accentuated itself today to the point where the car can not be driven.

I was driving with a full to 3/4 full tank today, engine temperature was fine all along, oil level a bit on the high side (just in case this is important information

).
I also saw that there are several posts online that describe this or similar issues, and after reading those I get the impression that there could be multiple reasons for this symptom... If so, maybe I should take the car to a mechanic and have a complete service on the engine? As you can tell, I am far from being an expert, so rather than completely screwing the engine, maybe this would be the wise thing to do...?

Extreedoc · Jan 20, 2018

Sounds like a blocked filter in the fuel line..., tank, I mean tank... It may seem strange to have these two opposite problems but it is quite possible to have both at the same time. I had this problem with my car, there was debris in the fuel tank which gathered around the filter on the pick-up pipe, when I got to a hill and needed plenty of power the engine bogged down because it was being starved of fuel. It would idle ok but full throttle was a no-no. The debris would fall away from the filter when the car was not running and all would be well until it gathered around it again next time I used the car. I fixed it by taking the filter off the pick-up pipe and installing an in-line filter with a see-through body in the fuel line at a place I could access. This filter could be changed when it clogged and soon the debris was cleared from the tank and all was well again.

Goc3k · Jan 20, 2018

I'd take the carb feed off and see how much supply actually comes out while the pump is running. Pathetic dribble = blocked lines/filter or possibly a bad regulator.

Good shout about the see through filter near the carb, makes it easy to keep an eye on things

nickjaxe · Jan 20, 2018

Hard to imagine why it didn't stop sooner or art worse the exhaust explode??

kyamon · Jan 21, 2018

Yes, checking the filter is something I certainly have to do. The filter itself is new, but before I got the car it has been sitting for several years, so who knows what kind of junk still is now slowly moving from the tank toward the engine...
@Goc3k The flow out of the gas line is strong, and the needle valve is new, so that seems fine. Plus, I did fill the engine with gasoline (and that did not take very long), so I believe that on average things up to the carb are good (except for the filter issue)

@nickjaxe Very good question... I guess I was lucky that the thing did not blow up. The power loss is not entirely new, but it was never as extreme as today.

Goc3k · Jan 21, 2018

i'd probably be inclined to pay a professional to restore the carb properly, especially if it had petrol in the bowl while it sat a few years (if you haven't already) - always really aggravating tinkering and tinkering with an old carb that at the end of the day really needs restoration, if you can get a manual for the carburetor though and can get a rebuild kit, it might be worth having a go yourself if you feel up to it as the stromberg 175 isn't particularly complicated as far as they go.

Extreedoc · Jan 21, 2018

Talking about the carb and the fact that it's been standing: have you checked the rubber diaphragm in the top? It could very easily be perished and stopping the piston from lifting which will severely limit your top-end power.

kyamon · Jan 28, 2018

I believe I found the issue - the little rubber tube on the connector of the pipe that connects the carb to the vacuum advance mechanism on the distributor was brittle (and actually broke, see below). I am assuming it was leaking really badly, so the ignition timing probably was completely off.
(@Extreedoc I believe I never replied to you: the diaphragm is OK, I did check it when taking the carb apart.)

Before I found this, I had decided (and started) to remove the cylinder head and make sure that the pistons, valves, and head gasket were OK. Other than the power loss I had no reason to assume that this was not the case, but I also just wanted to see the inside of my engine, and was/am hoping to improve things there as well

So now I have a follow-up question: the head gasket looks to be in perfect shape, so there is no worry there. However, the valves are covered with lots of crud, and - as far as I can tell - so are the valve seats. My impression is that the carbon buildup on the valves and seats were actually forming a seal, but I wonder if cleaning and lapping everything could substantially improve things (and, similarly, if the fact that I cleaned the valve could also now have damaged the "seal")? I am hesitating to do the lapping because this (as everything else) would be a first for me, and on the 6-cyl engine it is a bit of a pain to get the exhaust valves out without removing the engine block from the car (which i can not really do). As I wrote earlier, the engine has 35000 km, but before I bough the car last spring it has been sitting for nearly 10 years.

For the moment my plan is to replace the distributor, fix all the tubes and hoses (...), reassemble the cylinder head and see what I get. Does this sound like a reasonable approach or will it fail for sure?
(in the meantime I had fun installing new shock absorbers and parabolic springs on the rear wheels and remove the rusty sh** that was on there from before

)

Here are a couple of photos I took just after I removed the cylinder head. In the meantime I removed much of the carbon deposit from the pistons... The third of these shows the number I found stamped on the cylinder head - does this tell me anything (given that, as I understand, the serial number is on the engine block)?

Turboman · Jan 28, 2018

Goc3k said:
i'd probably be inclined to pay a professional to restore the carb properly, especially if it had petrol in the bowl while it sat a few years (if you haven't already) - always really aggravating tinkering and tinkering with an old carb that at the end of the day really needs restoration, if you can get a manual for the carburetor though and can get a rebuild kit, it might be worth having a go yourself if you feel up to it as the stromberg 175 isn't particularly complicated as far as they go.

At that mileage, there shouldn't be significant wear in the carb. I would have thought dismantling and thorough cleaning would sort it.
And, as above^^^^^^^^, replacement of all rubber bits.

Turboman · Jan 28, 2018

kyamon said:
I believe I found the issue - the little rubber tube on the connector of the pipe that connects the carb to the vacuum advance mechanism on the distributor was brittle (and actually broke, see below). I am assuming it was leaking really badly, so the ignition timing probably was completely off.
(@Extreedoc I believe I never replied to you: the diaphragm is OK, I did check it when taking the carb apart.)

Before I found this, I had decided (and started) to remove the cylinder head and make sure that the pistons, valves, and head gasket were OK. Other than the power loss I had no reason to assume that this was not the case, but I also just wanted to see the inside of my engine, and was/am hoping to improve things there as well
So now I have a follow-up question: the head gasket looks to be in perfect shape, so there is no worry there. However, the valves are covered with lots of crud, and - as far as I can tell - so are the valve seats. My impression is that the carbon buildup on the valves and seats were actually forming a seal, but I wonder if cleaning and lapping everything could substantially improve things (and, similarly, if the fact that I cleaned the valve could also now have damaged the "seal")? I am hesitating to do the lapping because this (as everything else) would be a first for me, and on the 6-cyl engine it is a bit of a pain to get the exhaust valves out without removing the engine block from the car (which i can not really do). As I wrote earlier, the engine has 35000 km, but before I bough the car last spring it has been sitting for nearly 10 years.

For the moment my plan is to replace the distributor, fix all the tubes and hoses (...), reassemble the cylinder head and see what I get. Does this sound like a reasonable approach or will it fail for sure?
(in the meantime I had fun installing new shock absorbers and parabolic springs on the rear wheels and remove the rusty sh** that was on there from before )

Here are a couple of photos I took just after I removed the cylinder head. In the meantime I removed much of the carbon deposit from the pistons... The third of these shows the number I found stamped on the cylinder head - does this tell me anything (given that, as I understand, the serial number is on the engine block)?

View attachment 140486 View attachment 140488 View attachment 140489

I should think the number on the head is just a casting number.

kyamon · Jan 28, 2018

OK, thanks. Glad to hear that I dont need to remove any valves!
Plan of action now is to replace the distributor and check/replace some more rubber.
On a side note - is it reasonable to keep a old head gasket, if it looks OK (not for this time, but maybe in the future...)?

Turboman · Jan 28, 2018

kyamon said:
OK, thanks. Glad to hear that I dont need to remove any valves!
Plan of action now is to replace the distributor and check/replace some more rubber.
On a side note - is it reasonable to keep a old head gasket, if it looks OK (not for this time, but maybe in the future...)?

No. New head gasket every time.

Edit. And you can check the valves by turning the head upside down, and pouring oil into the valve recesses.

Carb issue - fuel in cylinders

Active Member

Well-Known Member

Active Member

Well-Known Member

Active Member

Active Member

Active Member

Well-Known Member

Active Member

Well-Known Member

Well-Known Member

Well-Known Member

Active Member

Well-Known Member

Well-Known Member

Active Member

Mab An Gov

Mab An Gov

Active Member

Mab An Gov

Similar threads