3.5 intermitent hesitation under load

[classic77]

Hey All

I have a stromber carb 3.5 with 4 speed which starts fine first go hot and cold, idles fine, revs fine, drive otherwise perfect, has had new ht leads and fuel pump not long ago. But! has an intermitant hesitation when under load when under 2000k rev. only really notice it in 3rd and 4th up step hills cause it requires a lead foot to get the fault but have noticed it in 1st and 2nd occasionally. Looks like the fuel tank could be a bit rust, but symptoms don't seem to be a blockage... anyone else get similar???

Plugs have been checked and replaced no7, but no different.

[bee utey]

Hey All

I have a stromber carb 3.5 with 4 speed which starts fine first go hot and cold, idles fine, revs fine, drive otherwise perfect, has had new ht leads and fuel pump not long ago. But! has an intermitant hesitation when under load when under 2000k rev. only really notice it in 3rd and 4th up step hills cause it requires a lead foot to get the fault but have noticed it in 1st and 2nd occasionally. Looks like the fuel tank could be a bit rust, but symptoms don't seem to be a blockage... anyone else get similar???

Plugs have been checked and replaced no7, but no different.

Timing: give it a few more degrees advance, perhaps 6-8 BTDC. Remember your flat throttle is disengaging the vac advance, could be too retarded over all.
Plugs, heat range? Check the colour of the insulators, they should not be brown coloured, that is a sign of running too hot. Gap? no more that 0.8mm unless you have HEI.
What kind of ignition system are you running? Weak coil possible. Rotor button gap to cap might be excessive. Lay the rotor sideways in the cap, align centre, look for no more than 1mm gap. You can lengthen the brass strip with a block of steel and a small hammer to peen it flatter. (carefully!)

[PhilipA]

Has it got points or electronic?

The old dizzys with the little advance adjustment on the outside can get so much slop that its impossible to keep the points gap correct.
The only temporary cure is to fit with an electronic trigger.
I also agree with bee utey that the air gap can be too large. Dizzy caps and rotors should be replaced every so often 100KK?
Regards Philip A

[classic77]

Yeah cheers for the advice lads:)

The rig has boch ignition with points. NGK plugs. engine always runs on normal water and oil temp, so rekon your right on the vac advance and timing... in fact knowing the ranger its probably all the below!:confused:

Have to wait for the weekend to check it out... let u know what I find..:cool:

[UncleHo]

G'day classic77 :)

Could be a crook auto advance unit, there is a bloke that does exchange vaccy's in Caboolture and has a website, www.advancediaphamoptions (http://www.advancediaphamoptions) he may be able to help if it is the Vac advance unit. he replaced mine which was dead (elect dist on 85 model) and it is as good as gold :) you just need the model of the distributor.


cheers

[CSK]

Could be sticky valves, quite a common problem on RV8s. What octane fuel are you using? Try some Moreys Upper Cylinder Lubricant, can fix it sometimes.


Maybe try get a genuine Lucas dizzy cap and rotor has fixed a few problems like this.

[PhilipA]

The rig has boch ignition with points.


I would be surprised if someone would put in a Bosch distributor with points. AFAIk for those old cars the only way you could do it was to graft half a Bosch Holden dizzy to a Rover shaft.

Do you mean you have a Bosch coil? If so what number?

What does the label say on the side of the dizzy say, not something on the cap? Has it got a little knob on the front to change the advance??
Regards Philip A

[bee utey]

I would be surprised if someone would put in a Bosch distributor with points. AFAIk for those old cars the only way you could do it was to graft half a Bosch Holden dizzy to a Rover shaft.

Do you mean you have a Bosch coil? If so what number?

What does the label say on the side of the dizzy say, not something on the cap? Has it got a little knob on the front to change the advance??
Regards Philip A

I have seen a few Bosch points distributors fitted to Rover V8's, they were properly engineered and not a home bodge. I sold one recently on ebay to a forum member, it had an early Bosch electronic conversion fitted. The modern HEI version is the one marketed as a "Scorcher".

[classic77]

G'Day Lads,

For info... it runs a bosch coil with original dizzy.

Thanks for all the advice and tips.... turns out it was the bosch coil... as it packed up completely this morning. Put in a new GT40R. Starts and runs stronger, no more hesitation .... don't even need to choke on cold start any more.

Re the sticky valvs... I am useing a lead replacement with upper cyl lubricant and run premium. I've checked various fuel company websites, they rekon rover v8 of this era is safe with unleaded.. I expect the alloy heads would need hardended val seats from factory?

[PhilipA]

I expect the alloy heads would need hardended val seats from factory?

All alloy head cars have inserted valve seats which are much harder than those which cause problems eg seats just cut into a steel head like an old Holden.
Regards Philip A