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Air filter housing for HS4 [also need tuning help]

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RobSelina

RobSelina

Jedi Warrior
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Okay, trying to decide on an air filter for the newly installed SU HS4 on the 1500 /ubbthreads/images/graemlins/grin.gif

This car is fast road & racing, so flow is more important than filtering ability.


I presently have no spacers or any hardware to go between the carb and air filter assembly. I'm looking at the longflo foam filters from VB:

https://www.victoriabritish.com/icatalog/mg/0115.html

I assume they're the same as the foam variety from moss (just $5 cheaper)

https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=30184

Also considering the K&N option listed on the VB site.

Any preference between the two? As far as anyone knows, is any additional hardware required between the carb and air filter housing (ie - a stock spacer?) What about the part number for the K&N filter assembly? I'd like to price it locally....

Any other option I should consider?

BTW, mounted and plumbed the HS4 this morning and got my throttle and choke linkage working. After starting her a few minutes ago, first impressions are very positive /ubbthreads/images/graemlins/thumbsup.gif

For those interested - I had to redrill the mounting holes on the HS4 body (could have done it to my intake instead), fab up a new arm for the choke on the carb, and build an adapter for the throttle. Aside from a few minutes with the welder, nothing was out of the reach of a shade tree mechanic, and you can get the right choke arm from rimmerbros by the looks of it.
 
Re: Need to pick a filter for my single HS4

Been running a K&N for like forever. No idea on housing availability tho.
 
Re: Need to pick a filter for my single HS4

Alright, I hacked the old ZS air box to fit just to test her out. Now I need some help getting her running right. Figure I might as well figure out anything else I need before I place an order.....

I filled the dash pot with 10W40, roughly 1/2" above the damper column. I moved the piston up and down to ensure it was moving freely, seemed fine - would present resistance on the way up but would fall relatively freely. There only seem to be two real adjustments on the side of the carb: throttle position at idle and the fast idle screw on the choke. I set my idle to roughly 1000RPM and fast idle to around 1500 for the time being.

Mixture adjustment seems to be determined by the needle right? Is there any way to determine which needle I have?

Here's a general description of how she drives:
1 - pretty good power, accelerates freely.
2 - putting & backfiring on deceleration
3 - not very smooth at idle
4 - for the first two miles or so, it would hold speed pretty well. As the temp went up another 20-30 degrees (probably around 210F now), she started to stumble.


So I take it I have a lean condition?

I'm pretty sure the carb came out of a 1.8L MGB...

Any advice appreciated. I haven't checked my timing recently, but the plugs, wires, cap & rotor are all pretty new. Compression on all cylinders was good too.
 
Re: Need to pick a filter for my single HS4

Rob,

Do you have a heat shield? how about a pic of your set up? sounds like a maybe a manifold(s) leak? causing your backfiring on decelaration. exhaust all nice and tight? How did you balance the carbs? Have a uniscyn tool? Just some thoughts?


mark
 
Re: Need to pick a filter for my single HS4

No heat shield yet...

I was thinking about where I might have a manifold leak and I'm not sure how well the carb is sealing against the intake manifold. I reused the existing gasket between the carb and intake, but it was rather hard and had an indentation from the ZS. I suspect I have a leak there. I'll replace it before I do anything else.

Exhaust is nice and tight. Ran well with the ZS on it.

As for balancing the carbs, only have one, so no need. Here's a pic of the installation:

mgsu2.jpg
 
Re: Need to pick a filter for my single HS4

Okay, my trusty friend Google tells me I can adjust the fuel/air mixture by adjusting the jet nut at the base of the carb. This true? Any details I should know?
 
Re: Need to pick a filter for my single HS4

And google is right again. Yep, mix and idle and mix and idle. Idle should be 800 or so, adjust mix to suit that.
 
Re: Need to pick a filter for my single HS4

adust the Lower nut up to lean , down to enrichen. do not loosen the upper nut it holds the jet in place. But i am sure your trust friend google told ya about that.

mark

nice coolant hoses BTW
 
Re: Need to pick a filter for my single HS4

[ QUOTE ]
adust the Lower nut up to lean , down to enrichen. do not loosen the upper nut it holds the jet in place. But i am sure your trust friend google told ya about that.

mark

nice coolant hoses BTW

[/ QUOTE ]

Thanks Mark. The link I found was rather vague, but that's enough detail for me to get into trouble tomorrow /ubbthreads/images/graemlins/wink.gif
 
Re: Need to pick a filter for my single HS4

Alright, wind died down enough for me to play outside for a bit.

I adjusted the jet nut down until it was running good, though I think I went a little too far. I can't get the idle down to around 800, it's a pretty steady 1200-1300RPM right now with the throttle screw completely out. Runs very smooth and no more backfire on decel. Only issue is a slight hesitation when I hit the gas. I assume I'm running a little rich now. I'll play with it some more tomorrow.

As for the idle, I noticed there was a little play in the throttle shaft.... I assume I'm getting some air leaking though this causing the high idle? There an easy fix (hack) for this?
 
Re: Need to pick a filter for my single HS4

No easy fix, there are oversize shafts or bore and replace. That air leakage will effect low idle for sure.
 
Re: Need to pick a filter for my single HS4

been reading up on it and I don't think it'll bother me. Seems it only affects idle & near idle performance right?

I'm going to spray carb cleaner on the housing near the throttle shaft tomorrow and watch for an idle speed change. Want to figure out if that is the problem. It doesn't have much play, but I can feel it at certain throttle positions. Also read up on how to fine tune the fuel/air mixture so I'll get that closer.

Even with a few bugs, it's already working better than the ZS ever did /ubbthreads/images/graemlins/wink.gif

Thanks,
 
Re: Need to pick a filter for my single HS4

Only should effect idle if not too bad. You should not be able to feel through linkage, try to wiggle it with your fingers on the shaft with engine not running even. If you feel movement it is loose of course. While in there check your linkage from the pedel for slop some place that you can correct easly, seems you just might have a bit.
 
Re: Need to pick a filter for my single HS4

Nice installation there Rob. Just out of curiosity, what jet needle did you use? Or, if you haven't picked a specific one, what was the AUD number on the carb? I have an AUD465 HS4 (from a 1971 MGB) I bought off eBay, thinking I might do just what you are trying to do, but had no idea what needle to use.
 
Re: Need to pick a filter for my single HS4

Jack - my comment about play at certain throttle positions was with the carb out of the car. Basically I was opening the valve and wiggling it around. It moves a little side to side, but very, very little up and down. I'll check for leaks tonight.

Dave - pretty sure my carb was a front carb from a late model MGB, but I can't recall the details. As for the needle, running whatever was already in it. /ubbthreads/images/graemlins/wink.gif I have no way of confirming anything since the AUD tag on the float chamber doesn't have a stamp on it, and there is no little metal tag like there is supposed to be.

If someone knows an alternative method of identification I'd like to know it. The only significant mark is right above the intake mounting surface. It's stamped 4HF1 if I recall. THe one was mis-stamped by the looks of it, so it has a strong one and a weak one very close to it. Stamping could be read as 4HF11.

I'll double check that info when I get home.

Thanks,
 
Re: Need to pick a filter for my single HS4

Rob,

Side to side wiggle is not important at all. enjoy.
 
Re: Need to pick a filter for my single HS4

alright, had a nasty leak on the carb to intake gasket. I was mistaken in thinking the ZS gasket would work. It has a little cutout from the 1.5" opening that just slightly extended past the edge of the SU. Enough so to draw a substantial amount of air.

[oops]

Anyway, removed the gasket, used shorter mounting studs and refitted the carb with a little high-temp RTV for the gasket. Don't know if that's the best way to do it, but I figured it's worth a shot.

I'm letting the silicone cure completely (24hrs) before I start her up and try tuning the carb.

Hopefully tomorrow I can take her for a 'spirited' drive /ubbthreads/images/graemlins/laugh.gif
 
Re: Need to pick a filter for my single HS4

Allright, you got it now.
 
Re: Need to pick a filter for my single HS4

Alright, fixed my intake gasket leak and I'm one of the lucky ones who doesn't have an air leak around the throttle shaft /ubbthreads/images/graemlins/smile.gif

Played with the fuel/air mixture and got her running pretty good. Seems I either end up a little lean up top or a little rich at idle though, might have to look into other needle profiles at some point.

Right now, I'm pretty happy with it the way it is. It's very drivable, but I think I'm going to get some thick cork to make a pair of gaskets and some aluminum & reflective tape for a heat shield. That carb has a lot of vibration being transmitted to it and she was pretty toasty too!

All in all though, very worthwhile. I like how easy the SU is to tweak, even though I don't have it 100% right yet.
 
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