Rough running crossflow

[thebassman]

Hi, bit long winded but here goes, bought a Mk1 1300xl with a 1600 crossflow, came on twin 40s but running rough so changed to a new 32/36  Weber and ran fine but I had no history on the engine but it had a high pressure oil pump and fuel regulator so I thought the engine may have had some work done. Fast forward 2 years and the head gasket went, took the head off found steel rocker posts, big valve head and +.060 pistons, all seemed fine got the head lightly skimmed and reassembled ( new gaskets and valves ground in) Assuming after all the top end work that there must be a hot cam of some sort fitted but as the engine has not been removed I don't know which one it is. Engine starts and ticks over but falters under acceleration, I have set tappets at .015 both inlet and exhaust as a starting point but unsure as to what the timing should be, going to work on it this weekend, pal has suggested 14 degrees btdc would appreciate any help

Thanks, Jeff 

 

[thebassman]

P.S. checked the compression 40 to 50 psi on all 4 pistons.

[BaileyMex]

When you say it falters under acceleration, what exactly is it doing?

Losing revs or spluttering or something else?

I guess I'd be checking fuel pressure, it the regulator was set up for 40's that might need adjustment, or if it has an electric fuel pump is that working OK?

Or carb might need different jets etc?

Im sure someone more savvy will also chip in

[guido]

On this information you provided it is almost not possible to give any good answer. Inlet/axhaust valve setting is way off at 0.015 and both not the same at all.

0,010 exhaust and 0.08 on inlet even with fast road or rally cam. It is as i read, guessing due to your carburettor change mostly. Out of the box installment?

Edited July 24, 2025 by guido

[Miniliteman]

11 hours ago, thebassman said:

P.S. checked the compression 40 to 50 psi on all 4 pistons.

How did you measure that, as that is very low?

9 hours ago, guido said:

On this information you provided it is almost not possible to give any good answer. Inlet/axhaust valve setting is way off at 0.015 and both not the same at all.

0,010 exhaust and 0.08 on inlet even with fast road or rally cam. It is as i read, guessing due to your carburettor change mostly. Out of the box installment?

That's for a Pinto, this is a XFlow.

And delivery fuel pressure does not influence running as long as it is high enough to keep the float chamber full.

[BaileyMex]

31 minutes ago, Miniliteman said:

And delivery fuel pressure does not influence running as long as it is high enough to keep the float chamber full.

I only suggested that as I had a similar problem years ago, was OK pottering around, but on the motorway under load it was backing off, turned out to be a faulty earth on an electric fuel pump.

[thebassman]

Hi  sorry put wrong compression numbers should be 140/150 psi measured with garage tester which I borrowed. The valve settings were suggested by Piper Cams as the cam is unknown they suggested. 015 " for both as a starting point. Any other suggestions would be helpful also timing thoughts, was thinking 14 dogs before tdc.

 

[thebassman]

P.S.  Carb was out of the box but supposedly jetted for a 1600. Supplied by Webcom and was running fine before I did the head gasket.

 

[guido]

9 hours ago, Miniliteman said:

How did you measure that, as that is very low?

That's for a Pinto, this is a XFlow.

And delivery fuel pressure does not influence running as long as it is high enough to keep the float chamber full.

my mistake sorry  yes, mixed it up by the two engines. But i did not mention anything on fuelpressure, just asked if this carb was out of the box and put on engine.

Edited July 25, 2025 by guido

[Miniliteman]

2 hours ago, guido said:

But i did not mention anything on fuelpressure, just asked if this carb was out of the box and put on engine.

It was BaileyMex who commented on the fuelpressure.

Jeff: if the engine was running ok on this carb before then check for vacuumleaks around the inletmanifold / carb. Spray a bit of brake cleaner around the manifold-gasket area. If the rpm / running changes you have a vacuum leak. Also check the vacuumhose to distributor.

0.015" for both inlet and exhaust is a good starting point. So is a static ignition timing of 14 degrees BTDC.

[Vista Estate]

14 hours ago, Miniliteman said:

How did you measure that, as that is very low?

That's for a Pinto, this is a XFlow.

And delivery fuel pressure does not influence running as long as it is high enough to keep the float chamber full.

You are right @Miniliteman. Weber are sensitive to fuel pressure.

It should be no more than 3psi. And yes the compression should be in the region of 160 to 180psi for a 1600 xflow. 150 is a little low.

Vacuum leak is a possible problem usually the carb is not sealing right on the manifold.

It's worth checking the accelerator cable adjustment too and spring. The linkage can stick or lightly jam if not aligned. Finally the accelerator pump diaphragm on the carb may have a fault. If its been sitting for a while the diaphragm can get dry and the spring not move right.

What's the dizzy like too?

[thebassman]

Thanks for the tips guys, heading into the garage this afternoon so will look at all things mentioned.