Volvo Community Forum. The Forums of the Volvo Owners Club

Forum Rules Volvo Owners Club About VOC Volvo Gallery Links Volvo History Volvo Press
Go Back   Volvo Owners Club Forum > "Technical Topics" > PV, 120 (Amazon), 1800 General

Notices

PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars

Information
  • VOC Members: There is no login facility using your VOC membership number or the details from page 3 of the club magazine. You need to register in the normal way
  • AOL Customers: Make sure you check the 'Remember me' check box otherwise the AOL system may log you out during the session. This is a known issue with AOL.
  • AOL, Yahoo and Plus.net users. Forum owners such as us are finding that AOL, Yahoo and Plus.net are blocking a lot of email generated from forums. This may mean your registration activation and other emails will not get to you, or they may appear in your spam mailbox

Thread Informations

Need carburation advice double SUs SH6

Views : 2059

Replies : 39

Users Viewing This Thread :  

Reply
 
Thread Tools Display Modes
Old Dec 30th, 2018, 00:29   #1
adarvasi
Member
 
adarvasi's Avatar
 

Last Online: Mar 1st, 2022 01:17
Join Date: Sep 2018
Location: Mexico City
Default Need carburation advice double SUs SH6

Learned friends,

Slowly dealing with one issue at a time, but now it has become urgent that I solve a carburation issue: the engine starts instantly when cold with the choke out, then it starts to fail and dos not hold in idle, unles I pump the accelator to keep the rpm fairly high (around 1200).
Hen the engine is hot it just won’t start.
Mexico City varies en altitude between 7500 and 8500 feet, the car was setup at sea level, the linkage was painted and is hard to adjust, and I am in the process of obtaining new linkake.
When the car is running has a very stinky exhaust, which leads me to believe in an extra rich mixture.
I have a couple of books on how to set up the carburators, but I have been unable to find altitude related tips.
Your advice is kindly appreciated
Happy New Year to all of you
Andres
adarvasi is offline   Reply With Quote
Old Dec 30th, 2018, 03:32   #2
c1800
Master Member
 

Last Online: Mar 26th, 2024 23:41
Join Date: Oct 2013
Location: Alberta
Default

“Effect of altitude and climatic extremes on standard tuning

The standard tuning employs a jet needle broadly suitable for temperate climates from sea level up to 6000 feet. Above that altitude it may be necessary, depending on extremes of climatic heat and humidity, to use a weaker tuning. The factors of altitude, extreme climatic heat and humidity each tend to demand a weaker tuning and a combination of any of these factors would naturally emphasize this demand. Tills is a situation which cannot be met by hard and fast factory recommendation owing to the wide variations in the conditions existing, and in such cases the owner may have to do a little experimenting with alternative weaker needles until one which is satisfactory is found. To assist in this matter it is normal for a recommended weak needle to be listed.”


From this link.

https://sucarb.co.uk/technical-su-carburetters

I don’t know if this is what’s causing your problem. Hopefully others will chime in.
c1800 is offline   Reply With Quote
Old Dec 30th, 2018, 03:38   #3
c1800
Master Member
 

Last Online: Mar 26th, 2024 23:41
Join Date: Oct 2013
Location: Alberta
Default

Some more reading.

http://sportscarcraftsmen.com/tuning-for-altitude/
c1800 is offline   Reply With Quote
Old Dec 30th, 2018, 08:20   #4
c1800
Master Member
 

Last Online: Mar 26th, 2024 23:41
Join Date: Oct 2013
Location: Alberta
Default

And more from an MG article ( with SU’s)

“High altitude running:
I drive in mountains often enough to notice this effect fairly often. When driving up Pikes Peak in Colorado (USA), the entrance gate is close to 9000 feet, and the peak is slightly above 14,000 feet altitude. At 10,000 feet you have 30% less air than at seal level, and at 40,000 feet about half of the air that you would have at seal level. The most noticeable affect is like having an engine only half the size with very low compression ratio, so power output will be dramatically lower. The engine can still run okay, and it will still get you there, but you may need to catch a lower gear and stand on the throttle with a little more patience.

Driving the car to high altitude can cause the carburetors to run richer. As air pressure drops the air will be less dense, and it will require wider throttle opening to get the power you need to climb a hill. For a given mass air flow, the flow velocity will be higher with less dense air, and this will draw slightly excess fuel flow from the fuel jets, making the fuel mixture richer. To compensate for this effect you can turn both carburetor mixture nuts as much as two turns leaner when running to these altitudes, and reset the mixture leaner when returning to lower altitude.

This may be an acceptable adjustment if you regularly run at high altitude, but re-adjusting fuel mixture for frequent changes in altitude can be a pain. The car will usually run okay with richer mixture while you are on throttle, but will likely not want to idle in thin air. My easy fix for this is just to reset idle speed at higher altitude, and then set the idle speed back to normal once I get back down to lower altitude again. If you will commonly be running at high altitude, and not going down to sea level very often, it may be appropriate to install leaner (thicker) needles in your SU carburetors. “

Looks like you need to lean the mixture up to 2 turns, (12 flats). Start with one turn and see if you have any improvement.
c1800 is offline   Reply With Quote
The Following User Says Thank You to c1800 For This Useful Post:
Old Dec 30th, 2018, 11:45   #5
adarvasi
Member
 
adarvasi's Avatar
 

Last Online: Mar 1st, 2022 01:17
Join Date: Sep 2018
Location: Mexico City
Default

Great information C1800, thank you very much.
Will start experimenting later on today.
Best
Andres
adarvasi is offline   Reply With Quote
Old Dec 30th, 2018, 14:44   #6
arcturus
arcturus
 
arcturus's Avatar
 

Last Online: Today 09:21
Join Date: Mar 2006
Location: Sagres Portugal
Default

For what it's worth I suggest that you start off by checking which needles are fitted now. The number will be stamped in on the shank. Then go back to basic setting and start from there.
Attached Images
File Type: jpg su.jpg (332.4 KB, 11 views)
File Type: jpg su (2).jpg (333.0 KB, 8 views)
__________________
life's too short to drink bad wine

Last edited by arcturus; Dec 30th, 2018 at 14:52.
arcturus is offline   Reply With Quote
The Following User Says Thank You to arcturus For This Useful Post:
Old Dec 30th, 2018, 15:54   #7
blueosprey90
Master Member
 

Last Online: Today 16:06
Join Date: May 2017
Location: New Milford, Connecticut
Default

You may have several problems. I run H-6 carburetors on my MGA and I think these are very similar to the HS-6 except for the connection between the float bowl and the main carb body.

1) symptom is that the carbs die at idle: I believe this is caused by your carburetors being unbalanced; and at idle, the engine is running off of just one carburetor.

When you tune your carburetors, they need to be balanced. De-link the carburetors at the throttle shaft so you can tune them individually. My car has a W shaped spring linkage that is loosened. Balance the air flow into the carburetors with a Unisys device, heater hose to you ear or by other means. Basically the adjustment is made at the throttle set screw on each carburetor. Once balanced, the carbs can be re-linked at the throttle.

2) symptom is that the car is running too rich: The car is running too rich! Setting the jets at 12 flats (two full turns of the adjusting nut) is an OK starting point, but I don't find it very accurate. I follow a different procedure that you might use if you have a vernier caliper. I remove both dashpots and pistons from the carb body. If you look straight down into the carb bodies. you will see the top of the jet inside of the jet bearing. The distance between the top of the jet and the top of the jet bearing (these look like two brass circles, one inside the other) need to be exactly the same on both carburetors. The shorter the distance, the more lean the carburetor is running. I usually set my MGA at .08" (2.05mm), but depending on humidity and temperature, I run anywhere from .07" to .10" (2.55mm). I've found that it usually takes 1 to 2 flats to make a .01" adjustment and that the carbs do not adjust exactly the same.

Note: a) While you have the pistons out, identify and record each needle. They should both be the same. Record the needle type as you may want to change needles based on needle profile and the type of driving you do.

Note: b) Once you make both of the adjustments described above, you can fine tune by removing the dashpot damper caps and inserting a straw or piece of wire (equal lengths and bent to point at each other - i.e., "diving rods") in each. As you rev the engine, they should rise the exact same amount. If they don't, you need to fine tune. If I recall correctly, it is the air flow (balance) adjustment that you will revisit.

Note: c) When I set my bridge at .08", I am shooting for a lean setting. A lean setting makes the engine run hotter. I have exhaust gas temperature sensors and can monitor my exhaust gas temperatures. If I am running over 1350 degrees at wide open throttle, I adjust the carbs maybe one or two flats richer to bring down the temperature. Since you won't have these sensors, you need to learn to "read" your sparkplugs. A whitish, light tan color is what you want to see. A whitish grey color is too lean. A dark tan or black is too rich.

3) Symptom is that the car won't start when hot. This sounds like vapor lock. Do you have ethanol in your gasoline? What happens is that the heat from the engine causes the fuel to vaporize in the carburetor. At higher altitudes, I imagine that fuel vaporizes at an even lower temperature than at sea level. A heat shield, heat wrap on the manifold or duct work to bring cool air into the engine bay are potential solutions.

4) Tuning the carburetors is only one step. Make sure your timing is properly set and make sure that your valve lash is also properly set.



Just for reference, this is my journal description of my effort to tune my new PV444 running H-4 carbs. You'll see that it was multistep and somewhat of a trial and error method:

August 15, 2017: Partial tune. I got the car warmed up with the idea of checking valve lash. I hoped that I could bump the engine with a remote start button, but was unable to make the connections. So to turn the engine, I had to heave the car forward and back while in 4th gear.

Valves don’t move all that much. All of the exhaust valves were too tight and I adjusted to 0.18”. The intake valves were a bit loose, but I mostly left them alone. The intake valve lash spec is 0.16”. (Note: these were the B-16 spec, not the B-16B spec.)

Plugs looked very sooty, with possible exception of #4 Cleaned those up.

I took the dashpots off the carbs and measured the distance between the jet and the top of the bridge. The rear carburetor was set at .135”, the front one at about .13”. I reset the jets on both carburetors to .10”. One flat seemed good for about .01”. I may lean them out further by one flat to bring them to .09”. We’ll see how it runs for now.

The pistons had carbon soot on the engine side, evidencing that there had been backfires into the carbs as I had suspected.

I tried to balance the carbs. At idle, it seemed as if the engine was running on just the front carb. Because I didn’t want to take off the air filters, I balanced using those “divining wires“ that go into the top on the piston when you take out the damper caps. The engine really wanted to run on the front carb, but eventually I think I got them balanced.

… Seemed to run better, smoother. …

August 20-29, 2017: Engine Tune up. 67,660 miles. New spark plugs NKG 6HS. Pulled the distributor and did a proper job on the points. Filed down both faces until smooth and reset points gap to .018”. I think the flywheel is off by 180 degrees. (Actually it was the distributor drive gear) With that assumption, I set the static timing at 6 degrees before TDC with rotor pointing to 2:00 rather than 8:00. A shot of starting fluid into the carbs, and it fired right up.

I let it warm up and reset the valve lash to 0.020" for both intake and exhaust. Car seemed to idle on the fast side. Using a dial back timing light, the advance at idle was about 28 degrees. Too far advanced.

I removed the air filters from the carburetors. Engine seemed to be running off of the front carburetor only. Attempted to synchronize the carbs using a Uni-Syn device. Very difficult to get them balanced, but eventually I got close. Leaned out the carbs one flat, so jet should now be below the bridge .09” rather than .10”.

Set the timing at 20° before TDC using a dial back timing light at “fast idle” I’d guess I was at least at 1,500 to 2,000 rpm. And at idle, it read 5° before TDC which I thought was a bit low. AARGH! I need a better system! Checking the manual after the fact, I see that I should have set the advance at 23° to 25° before TDC. Revisited and corrected.

September 3, 2017: I revisited the timing and reset to 24° before TDC by timing light.

Last edited by blueosprey90; Dec 30th, 2018 at 16:21.
blueosprey90 is offline   Reply With Quote
The Following User Says Thank You to blueosprey90 For This Useful Post:
Old Dec 30th, 2018, 21:57   #8
adarvasi
Member
 
adarvasi's Avatar
 

Last Online: Mar 1st, 2022 01:17
Join Date: Sep 2018
Location: Mexico City
Default

Thank you Arcturus for the suggestions and info attached

Last edited by adarvasi; Dec 30th, 2018 at 22:00.
adarvasi is offline   Reply With Quote
Old Dec 30th, 2018, 22:08   #9
adarvasi
Member
 
adarvasi's Avatar
 

Last Online: Mar 1st, 2022 01:17
Join Date: Sep 2018
Location: Mexico City
Default

Great detailed info Blueosprey,
Tomorrow will be a “Tune up day”
It is very interesting that these are the exact principles utilized in flying a piston
airplane, the engines are really turn of the last century conceptions, the only concession to modernism being mechanical fuel injection. The advantage though, is that the mixture control asjustment is inside the cockpit. But exhaust temp, leaning for altititude, vapor lock, etc are concepts that I am very familiar with.
Again, thanks a lot for very valuable information
Happy new year
Andres
adarvasi is offline   Reply With Quote
Old Dec 31st, 2018, 10:19   #10
arcturus
arcturus
 
arcturus's Avatar
 

Last Online: Today 09:21
Join Date: Mar 2006
Location: Sagres Portugal
Default

I tried to balance the carbs. At idle, it seemed as if the engine was running on just the front carb. Because I didn’t want to take off the air filters, I balanced using those “divining wires“ that go into the top on the piston when you take out the damper caps. The engine really wanted to run on the front carb, but eventually I think I got them balanced.


That got me thinking. If I could get access to a lathe I would turn out two "plugs" that would fit snug after removing the damping plunger, bore a hole in the center and insert a rod with calibration markers. The rise and fall of the rods would allow me to balance the carb air flow without the balls aching problem of removing the air filters on theB16b, H4 carbs.
__________________
life's too short to drink bad wine
arcturus is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 21:46.


Powered by vBulletin
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.