Amazon: 123GT carburetors

[Jayrob79]

Good day all!!!
I’m currently exploring carburetor options for my 1967 123GT. The Twin SU carbs don’t seem to perform very well with my cam and exhaust. I’m considering the Mikuni HSR 42 set up. I don’t go to the track, I just like to drive the canyon roads here in Colorado. Any advice would be greatly appreciated.

Jeff Robinson

[c1800]

Have you had the SU’s rebuilt professionally? Throttle shaft/spindle wear is common, which allows a vacuum leak, and poor performance. Properly rebuilt and tuned SU’s will be more than adequate.

Search this forum for SU carbs and Mikuni and you’ll find some discussions.

Joe Curto is often mentioned as a good option for rebuilding.

http://joecurto.com/services-offered


Tom Bryant also referenced regularly

https://thosbryant.wordpress.com/faqs/

I have no experience with either.

Good luck.

[classicswede]

Your carbs are most likely worn, possibly wrong dash pot oil and also might need a change of needles.

What cam and exhaust do you have and any other supporting mods?

[Ron Kwas]

Jeff;

Welcome to this forum!

"Twin SU carbs don’t seem to perform very well with my cam and exhaust" it seems to me a sweeping, unsubstantiated indictment of your carbs for your very first posting...before you do this, there is a lot of information you need to give,...on yourself and level of vintage Volvo (and SU) experience and your car, before we can agree with your indictment that your carbs are to blame for lack of performance, and that they need work or replacement...

Tell of yourself: What is you level of technical or vintage Volvo experience? Have you had this car long? Have you driven a 123GT in good condition and know the level of performance you can reasonably expect from it? ...or have you just acquired this car (from a barn, with 20 year old fuel in the tank and a mouse houses possibly clogging both Air-Filters and exhaust, and a dragging Emergency Brake?) ...and expect "modern and contemporary" performance from it, before you've even done an ignition and carb tune-up? Is your Distrib Centrifugal Advance free and functional? Do you know an SU carb from a (insert a completely unrelated term here...example: Hole in the ground, Orgasmatron, ...)? Do you know what Dashpot Damping Fluid is and where to put it? ...have you or previous owner made any changes from factory stock (would you know them if you saw them)?

Give existing conditions: Condition of engine (stock? mileage?, Cam, and condition?), Manifolding? Exhaust? Old or fresh fuel? State of Ignition Sys tune?

Don't take this wrong (my intent is not to beat you up at you first visit!), but before we (I anyway) can give any sort of useful info or help, I need to know a lot more of whom and what I am dealing with. Fact is, the 123GT was a very good performing car for its day, and quite reasonable for today even, so before you go and "upgrade" parts, you would be well advised to first bring the existing stock parts to their original function and performance...you might then find that you will like the car for what it was then and can be again now...without "upgrades"...

Cheers from Connecticut!

[amazon69]

Well done Ron for finding a way to bring SU carbs and orgasmatrons into the same sentence. Possibly a world first.

[tdz840]

Ive run both SUs and side drafts on my 1967 1800. The SUs were tweaked significantly with needles optimised to my engine and a damping spring and oil to suit.
However, before any of this tweaking occurred i got the basics right, ignition, fuel and air.
For example early on I decided to fit a 123 ignition. Probably no better than a well set up bosch distributor the fact remains that a 50 year old dizzy wont be at the same condition Bosch intended. For example there is a degree of adjustment on the centrifugal advance weights that Ron mentions. Dont bother, almost certainly will fracture when the metal gets a sniff of a set of pliers and i defy any one to accuratley bend both sets to the right degree. Of course with a 123 its just click on a PC.
For a standard 123GT i would reccomend sticking with the SUs, certainly over the hype and greater difficulty getting spares. I doubt that the cost of fitting alternative carburettors will see the gains you wish.
I fitted side drafts to an engine that had significant rework and components matched to that rework. General wisdom i understand is up to 130-135hp(fwhp) SUs are your best bet. Your current set up is likely to be just below that level. Above 140-145hp you start to transition to one carb per cylinder to aid the free flowing exhaust you would have fitted. Side drafts have infinite adjustment (ask how I know😂&#128514 on the four plus circuits. For example the accelaration pump can be tweaked to an ounce of its life, whereas SUs....dont!
The side drafts are a bunch of fun, not just the noise but the immediacy of the power (and I know SUs can be made to achieve this but no way like side drafts). Fuel consumption pro-rata for a well set up system is on par with SUs-fact.
So in summary- what are your ambitions for your engine. More or less the same then stick with SUs and get the basics right. You will be surprised how great a well set up system is.
If you intend to upgrade the engine significantly over the OEM set up; volumetric efficiency, cam, significant headwork and inlet and exhaust then change to side drafts (or throttle bodies) may be your answer.
I like to tweak but beware its addicative and the closer to your goal its governed by the law of diminishing gains compared against the law of increasing costs.
Russ
PS looking for HSRs from a well known source - caveat emptor.

[Jayrob79]

A big thanks to everybody for your replies. I’ll try to address all inquiries in this post.
My mechanical knowledge is pretty extensive, however my experience with vintage Volvo’s only goes back to last year when I inherited the 123GT from my uncle. I have owned vintage mopars, and VW’s in the past. I have been tuning my own vehicles since I was 10 years old which is when my parents had a Volvo 240. I kept it running until I was 20 years old and then the transmission gave up. I’m a big fan of air, fuel and fire troubleshooting. However I also know how to set valves and timing. I am new to SU carbs but I learned how to sync them via the old SU handbook that my uncle had in the car. That’s my car history in a nutshell, now for the 123gt history.
The 123 was purchased by my uncle 10 years ago. He completely stripped it down and rebuilt the entire car. He traded the original b18 for a b20 and had it rebuilt. He had a k-cam installed, bored the cylinders to .03 over. The head was rebuilt too however no performance upgrades were done to it. He sent the original carbs out to a professional for rebuild. They are the 3 bolt su’s. My uncle had the car in California, however I live in Colorado at 6000’. That being said I set the air fuel mixture for altitude and advanced the timing 5 degrees. I also installed a 2-4 psi electric fuel pump only because the fuel was evaporating before it got to the mechanical pump, but the motor still ran. I concluded that the horrible ethanol in our gas was the cause of evaporation. I changed the filter and flushed the tank out and found a non ethanol gas station close by. The 123 ran much better with the work I had done but I still noticed a lack of pick up on the hills around here. Since then I added some octane boost the the gas tank. It seemed as though I woke the sleeping dragon at that point. As far as the dash pots go I was using ATF but that stuff would disappear quickly so I switched to 15w-50. That gave me better throttle response. I don’t expect the 123gt to behave like a modern vehicle in any sense however with a 2 liter twin carb motor producing 115-120hp it should move pretty quick. It has a 4-1 exhaust. It has the pertronix ignition upgrade in the distributor. I could advance the motor a bit more but I think 15 degrees should be enough. I was thinking about getting some lean (altitude) needles for the carbs but I don’t know where to get those from. That’s why I was looking into the Mikuni HSR-42 carb set up from v-performance.
My plans for the car are to enjoy the canyon roads here in Colorado. All in all the car runs good now unless you are climbing a hill. There should be enough available horse power with the current set up to gain speed on a long incline.
Thanks for welcoming me to the forum and I look forward to any responses.
Take care
Jeff

[classicswede]

If you like to gamble your money then spend with V performance. A lot never see the parts they ordered.

Burlin Fuels in the uk are the go to guys for SU's and would be able to recommend suitable needles. You could even go a little thicker with your dashpot oil if you wanted.

Timing I never check what the angle is, I just adjust for best running and the dizzy lands where it lands. As fuels are not what they used to be and dealing with worn components I only go and check angles if I'm having unexplained issues

[tdz840]

Originally Posted by classicswede

If you like to gamble your money then spend with V performance. A lot never see the parts they ordered.

Burlin Fuels in the uk are the go to guys for SU's and would be able to recommend suitable needles. You could even go a little thicker with your dashpot oil if you wanted.

Timing I never check what the angle is, I just adjust for best running and the dizzy lands where it lands. As fuels are not what they used to be and dealing with worn components I only go and check angles if I'm having unexplained issues

Sensible advice Dai, no two engine is the same and the needles on offer are only really a baseline. Its why i like side drafts and the ability to easily change jets, asses the changes then move on. With needles the jets are effectively located on the taper, difficult to see where the piston is under load in a real world situation and a lot of faffing getting the exact needle.
With jetsyou get within 10 then uses drills to optimise further.
Grinding needles on a drill press cant be done on the side of the road