Rover V8 vacuum issue
Discussion
Can someone advise where is best to ask this question, either in here, or a marque-specific sub-forum? It's to do with the Rover V8 engine but the question is generic to that engine rather than the car it's fitted in...
I bought this vehicle knowing that it wasnlt running well so have set about trying to find out why. I remembered that the standard inlet manifold on the Rover V8 feeds across the block, ie the RH carb feeds the two "end" pots on it's own side and the two middle pots on the opposite side. On that basis I've established that the RH (ie offside) carb isn't fueling at all.
To complicate the matter, the engine has LPG fitted. I was told that it had been running fine on LPG but not used petrol for along time. So at the moment I'm focusing on getting it running properly on LPG.
Using the above rule on which pots each carb feeds, I pulled the HT leads off for the pots which the RH carb feeds, and for all four, it made no difference at all. So I don't think that carb is fuelling at all. Now, it could be something to do with the LPG feed (which I'm not familiar with, and which is a pain because whereas you can see if a carb is getting petrol, you can't see whether it's getting gas!) but the one key thing I have found is that if you remove the air filter entirely and put your hand over the carb inlet, the LH carb (the one working properly) has masses of vacuum at tickover, whereas the RH carb, whilst it has some, has a LOT less.
I guess lack of vacuum could be down to piston and/or valve problems, but it seems unlikely that 4 cylinders spread between the two banks would all have a problem, and the other 4 not? I'll do a compression test when I can get hold of the right size adaptor (my compression tester is missing it's adaptor having not been used by me for about 10 years and having been lent out in the meantime) but are there any other obvious places I can look for vacuum leaks, or are there other well-known causes of low vacuum? I've had a good look around but in the absence of either a hole or a high-pitched whistle, I'm a bit stumped.
I bought this vehicle knowing that it wasnlt running well so have set about trying to find out why. I remembered that the standard inlet manifold on the Rover V8 feeds across the block, ie the RH carb feeds the two "end" pots on it's own side and the two middle pots on the opposite side. On that basis I've established that the RH (ie offside) carb isn't fueling at all.
To complicate the matter, the engine has LPG fitted. I was told that it had been running fine on LPG but not used petrol for along time. So at the moment I'm focusing on getting it running properly on LPG.
Using the above rule on which pots each carb feeds, I pulled the HT leads off for the pots which the RH carb feeds, and for all four, it made no difference at all. So I don't think that carb is fuelling at all. Now, it could be something to do with the LPG feed (which I'm not familiar with, and which is a pain because whereas you can see if a carb is getting petrol, you can't see whether it's getting gas!) but the one key thing I have found is that if you remove the air filter entirely and put your hand over the carb inlet, the LH carb (the one working properly) has masses of vacuum at tickover, whereas the RH carb, whilst it has some, has a LOT less.
I guess lack of vacuum could be down to piston and/or valve problems, but it seems unlikely that 4 cylinders spread between the two banks would all have a problem, and the other 4 not? I'll do a compression test when I can get hold of the right size adaptor (my compression tester is missing it's adaptor having not been used by me for about 10 years and having been lent out in the meantime) but are there any other obvious places I can look for vacuum leaks, or are there other well-known causes of low vacuum? I've had a good look around but in the absence of either a hole or a high-pitched whistle, I'm a bit stumped.
I believe that there is a Rover V8 forum on the web, decicated to all Rover v8 engines no matter what they are in, might be of help.
Here - its a general V8 forum but loads on Rover -
http://www.v8forum.co.uk/forum/index.php?sid=9c191...
Here - its a general V8 forum but loads on Rover -
http://www.v8forum.co.uk/forum/index.php?sid=9c191...
I signed up and posted on the V8 forum but had no responses, so if anyone here can help, here is what I posted, with slightly more up-to-date information:
The vehicle is running an ex-Range Rover 3500 V8 on Stromberg 175 carbs, along with an LPG conversion. It was sold as "running fine on gas, but really badly on petrol". The actual version was that it started and ran on gas, but not very well, and not on petrol at all.
I started looking around and trying to find the problem, and found pretty quickly that the 4 cylinders which the RH (offside) carb feeds were not running at all (ie 2,3,5 & . I haven't yet been able to work out whether the gas is getting to the mixer ring OK, but I assume it is as the gas comes off the vaporiser and splits just before the carbs. I can check that by swapping them over anyway.
The strange thing is that if I remove the air filter and put my hand over the intakes, the vacuum/suction is MUCH (and I mean MUCH) stronger on the nearside carb, the one which is running. I've done a compression test and the values are pretty even across all 8 pots at around 135 psi - probably a little low but this was stone cold, throttle closed, no oil down the barrels, and was done mostly to look for any major differences. Also I believe the old Rangie motor was the low-comp version anyway (?).
I also took the LPG mixer rings off and rigged up a temporary petrol supply to try and run it solely on petrol but it wouldn't start at all.
I've had a hunt around for vacuum leaks and not spotted anything yet. So I guess the next step is to strip the carbs and clean everything out and start from scratch.
Also the various breathers have all been completely chopped about - some are missing completely, some are blanked off (with bolts!) and so I need to work out how that all needs to be put back in place as well. But would this affect the general running?
The vehicle is running an ex-Range Rover 3500 V8 on Stromberg 175 carbs, along with an LPG conversion. It was sold as "running fine on gas, but really badly on petrol". The actual version was that it started and ran on gas, but not very well, and not on petrol at all.
I started looking around and trying to find the problem, and found pretty quickly that the 4 cylinders which the RH (offside) carb feeds were not running at all (ie 2,3,5 & . I haven't yet been able to work out whether the gas is getting to the mixer ring OK, but I assume it is as the gas comes off the vaporiser and splits just before the carbs. I can check that by swapping them over anyway.
The strange thing is that if I remove the air filter and put my hand over the intakes, the vacuum/suction is MUCH (and I mean MUCH) stronger on the nearside carb, the one which is running. I've done a compression test and the values are pretty even across all 8 pots at around 135 psi - probably a little low but this was stone cold, throttle closed, no oil down the barrels, and was done mostly to look for any major differences. Also I believe the old Rangie motor was the low-comp version anyway (?).
I also took the LPG mixer rings off and rigged up a temporary petrol supply to try and run it solely on petrol but it wouldn't start at all.
I've had a hunt around for vacuum leaks and not spotted anything yet. So I guess the next step is to strip the carbs and clean everything out and start from scratch.
Also the various breathers have all been completely chopped about - some are missing completely, some are blanked off (with bolts!) and so I need to work out how that all needs to be put back in place as well. But would this affect the general running?
Lots of later rv8 knowledgeable people on the tvr section although most were fuel injected. I'm sure someone may remember the days of carbs and would be willing to offer help. A post in the general section and someone may bite.
Unfortunately I don't know my way around the engine well yet so cant be of any more help.
Good luck
Unfortunately I don't know my way around the engine well yet so cant be of any more help.
Good luck
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