Twin HS2 Carb needles

[Hercplt]

Nope.  Well, yes I do, but its an old points type and was quite old anyway...

I've decided to bite the bullet and remove the twins and re-install the HIF44 that it was built with in the first place.  Its a free effort, and if the condition persists then at least I will have learned something new.

[94touring]

I took my twin hs4s off and put a hif44 on.  The twins were just too fussy to get perfect. 

[Jimini II]

Nope.  Well, yes I do, but its an old points type and was quite old anyway...

I've decided to bite the bullet and remove the twins and re-install the HIF44 that it was built with in the first place.  Its a free effort, and if the condition persists then at least I will have learned something new.

Sometimes when more than one item has been changed you just need to go back and change the old items back to the original ones one at a time to see where the problem is.

[Hercplt]

So HIF44 runs on choke... but barely... dies with any throttle... still misfires.  Often won't fire at all, but the coil produces spark as well as plugs.  Wondering if the coil just isn't doing enough.
Going to check compression next... maybe switch the coil with one that I know works on my dad MGB.

... the adventure continues...  8.gif

[MiniDave]

OK so you've ruled out the carbs as the problem.....if you don't have a massive air leak it has to be elsewhere.....I agree - check compression - if that's good swap the coil

[Jimini II]

If swapping out the coil does not work I guess you need to install the old points distrbutor.

[Hercplt]

I re-installed the twins, and for about an hour I had it running well. (not driving as I need a new throttle cable)... anyway, it ran and revved in the garage just fine.  Some hesitation here and there, but nothing like before.

Now it won't start.

However, when cranking, if I use my fingers and lift the dashpot pistons it will fire and try to run... but not run on choke or throttle.

The coil tests fine (3ohm, 9800oms and 12V where it needs it)... It ran good so timing must be at least ok.  Electronic dist looks good...

The fellow (Brit Ex-pat / mechanic) that put it together for me suggested that the carbs may be too small and not allowing enough fuel-air mixture through the carbs.  What the hell am I missing?!!

I mean really... large bore 1275's with worked head can run twin 1.25s... why can't my 998?

He thinks the cam is too hot... but I'm not sure.  Its a APT (Visard) VP7, which according to the spec sheet is suited to all A series, mild road cam (1500-7000 rpm).  Engine is +60, head is 12G295 with opened chamber / ports and large valves.

I think this is a starting issue, rather than a running issue now...

What am I missing?

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[cstudep]

These other folks are a lot more knowledgeable than I am on these things so I would only take this for what it's worth, which probably isn't much. I was having similar issues to what you are describing here, I have a 1275 with a 266 fast road cam and I could not get it to run consistently at all, one minute it runs fine, next it would not start, then it would back fire and carry on, always drove like crap.

New plugs, new wires, new cap & rotor, adjust valves......still the same. Changing out the coil, points, and condenser fixed it. Not sure which of the 3 it was since I changed them all at the same time but it starts flawlessly now and runs well for the most part. I think it was the coil but didn't want to push my luck by swapping it back to see.

I have dual HS4's which is way too much carb for my setup so getting that tuned properly is where my problems now reside. If you ever want to sell the HIF44 I am in the market for one LOL.

[Jimini II]

I re-installed the twins, and for about an hour I had it running well. (not driving as I need a new throttle cable)... anyway, it ran and revved in the garage just fine.  Some hesitation here and there, but nothing like before.

Now it won't start.

However, when cranking, if I use my fingers and lift the dashpot pistons it will fire and try to run... but not run on choke or throttle.

The coil tests fine (3ohm, 9800oms and 12V where it needs it)... It ran good so timing must be at least ok.  Electronic dist looks good...

The fellow (Brit Ex-pat / mechanic) that put it together for me suggested that the carbs may be too small and not allowing enough fuel-air mixture through the carbs.  What the hell am I missing?!!

I mean really... large bore 1275's with worked head can run twin 1.25s... why can't my 998?

He thinks the cam is too hot... but I'm not sure.  Its a APT (Visard) VP7, which according to the spec sheet is suited to all A series, mild road cam (1500-7000 rpm).  Engine is +60, head is 12G295 with opened chamber / ports and large valves.

I think this is a starting issue, rather than a running issue now...

What am I missing?

50.gif

Just a long shot here.
When you installed the twins did the manifold come with two locating rings that match up to the ports in the cylinder head?
If not just using the locating studs on a ported or normal head can be hit or miss, it is very easy to miss align the intake manifold to the head and you end up with air leaks.

[Hercplt]

Yes the intake has the locating rings...

[Hercplt]

Hazzaa!!!  Success! 62.gif

Replaced the plugs with NGK non-resistor type... and reset the twins per the SU website... Back to M needles with blue springs... Revs, runs and drives with only a slight hint of hesitation.  The plug leads were loose.. tightened them up.  Reset the timing by feel for now.  Totally psyched that I was able to run it 50km+ today all over town!!  Popped and missed often enough to know that its not quite right, but cruised along at 60-70Mph.  Part throttle in cruise or mild load and its doing well.

Long hills are a problem, as it bogs down and I end up plodding along up the hill in third.  I seem to recall years ago with the HIF44 carb that this was not a problem... You think that the Twins are the problem?  Its a VP7 cam (256??)

Anyway.. tonight is a success and having a beer in my Mini's honour... Cheers all for the advice these past few months!!!

Rich

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[BruceK]

WooHoo.   Congratulations

[cstudep]

Good to hear you got it running better. It's always a good feeling when something just works like it should.

[Hercplt]

Thanks... I don't know that it "works like it should"... at least not completely.  But I am happy for now.

Thinking I need a set of 1.3:1 rockers... re synch the twins, get the timing dialed in...

Long term... lose the VP7 and swap it with an SW5.

[Hercplt]

Questions... always more questions...

So, with the car running like a champ.  I did a compression test. approx 90-95 psi across the board.  My Brit mechanic guy says to give it some time, as we spent a lot of time cranking unburnt fuel through the engine... I mean lots...  He expects that over time it should get better.

Car runs great, but taps out at 100kph (was doing 120+kph years ago).  Up any hill, it just does not have enough power to even maintain speed let alone accelerate.  With WOT it tends to mis and hesitate badly.  So, yes I know I need a WB set up...

I presume that lack of power is compression related... and the wot hesitation is mixture?  75% throttle is great (except up a hill).

Thoughts?

[94touring]

That is pretty low compression, about half what I produce.  Even still if you're air/fuel is off you're going to be running like crap.

[MPlayle]

I agree with Dan that the compression seems too low. 

I am used to seeing around 150 in most of my basic Minis running mostly stock engines.

My Mini Marcos is a performance engine from Seven and it is around 200 on all cylinders.

[MiniDave]

So it used to do 120KPH with the same cam, carbs and rockers, and now it doesn't?

Or have you changed some of those things too?

I hope you haven't worn out the rings, but to test the theory you could pull the plugs, run a cold compression test, then squirt a bit of oil in the cylinders, crank it over a bit and run compression again. If you see a substantial gain - I would be somewhat concerned - if you don't I would be even more concerned!

[Hercplt]

So it used to do 120KPH with the same cam, carbs and rockers, and now it doesn't?

Or have you changed some of those things too?

I hope you haven't worn out the rings, but to test the theory you could pull the plugs, run a cold compression test, then squirt a bit of oil in the cylinders, crank it over a bit and run compression again. If you see a substantial gain - I would be somewhat concerned - if you don't I would be even more concerned!

The twin carbs are the change...  The engine wasn't very old (miles since rebuild).  He opened it up to do the seals etc (it sat in storage since '06)... everything looked good inside.

Can you explain the oil in the cyl trick??  why and whats the difference with each result?

Edit:  Its not blowing any kind of smoke (blue or grey)... at all... so its not burning oil past the rings as far as I am aware.

Rich

[MiniDave]

Squirting some oil down the bores and cranking it over (so the oil is distributed around the cylinder) will seal leaking rings up tighter, so the compression goes up. Which means the rings are worn. If the compression doesn't go up it either means the rings are so worn that it can't bridge the gap or there's something else wrong.

[Hercplt]

ok... Cold test;

1.  105
2.  80
3.  90
4.  100

With oil after cranking..

1.  115
2.  90
3.  100
4.  105

[MiniDave]

Not much improvement, maybe time to pull the head? I don't think given those results that there's anything that will improve with time and running.

[tsumini]

I had similar problems with my 850. Hard to start no power etc. 0-60 mph was 37 sec about 10 sec over spec.
It ran great with no load but was not consistent. Couldn't figger out if carb or ignition was the problem.
Finally took compression as follows:
1.105
2.85
3.120
4. 80
Took the head off and found exhaust valve on #4 and #2 was not seating and showed gaps in  the contact area and was obviously leaking. I hand ground the valve and seat of both 2 and 4 with valve grinding paste until full contact was achieved. I also honed #1 since it was slightly low compression.
Back together again the compression improved as follows:
1. 118
2. 112
3. 118
4. 130
Car ran great after this 0-60 mph improved to 21.6 sec better than spec. It ran great under load. And also started flawlessly. I also installed a Pertronix electronic ignition which improved performance.
As others have pointed out your compression seems to be too low.

[Hercplt]

Thanks for the info guys!  Much appreciated.

I don't mind doing a valve job in the end... it seems less messy than redoing the rings.

will keep posted...

[Hercplt]

Pulled the head today, and this is what I found.

The similar low comp on all 4 makes sense now... Kinda surprised that the gasket did this, as its basically brand new.

Pics to follow...

Would welcome opinions on the cause of the leaks, and opinions on what gasket I should use.  I have new copper type here that I can use.

Rich