How to tune twin Dellorto or Weber carbs 3 easy methods explained - Alfa Romeo GTV 2000 Bertone

Please Subscribe for more videos different methods explained for the home mechanic brought to you by #Alfatechniks thanks for watching please like!

[@toninaude1552]

Brings back happy memories of the hours I spent trying to tune my 1750👍🏻

[@alfatechniks887]

You and me both, hope you were able to set them up, practice makes perfect

[@rolanddemeyer8856]

I worked on alfa romeo for 20 years, 4 cylinders and later gtv 6 engines..the best scounding ever and again use golden lodge sparkplugs

[@alfatechniks887]

Which Golden Lodge spark spark plugs are your preferred choice? I run an MSD capacitive discharge system so it’s got to be suitable for the temp range

[@idontcareaboutyou7757]

@@alfatechniks887 what ???? MSD capacitive what? never heard of that

[@andyMSH700]

Clever clogs...some smart tricks here that I have never seen. Hose pipe and Temp on exhaust manifold.......you learn something new every day. Just hope i dont forget it :) Those webbors look mean.

[@alfatechniks887]

Thanks for the feedback Andy. Glad you liked the video. Oh and they are Dellortos! Do you have something similar which you drive?

[@andyMSH700]

​@@alfatechniks887 Ah ok, they look great....in the UK and ireland most Alfa cars rusted as the weather here is unkind so difficult to get as many oldies as other makes which is a pity. Yours is a beauty and rare over here plus very expensive if you do manage to source one. The Alfa's were something else. Yes, i have an old 1970 TR6 with fuel injection so easy to setup due to a common metering unit.

[@antoniosilveira1564]

That's nice. By the way, I used to keep the buterflies with same opening, using the smallest filler gage, before installing the carbs. Only play with four screws until get it accelereted, then lower the revs to 500rpm. The bubble sound and water drops on exhaust. Was amazing 🙂

[@antoniosilveira1564]

I never see anyone tunning and keep at lower revs. All at 1000rpm,😤 perhaps, because it is a challenge to keep it balanced. At 500 rpm the engine tells you how he feels. Only need to be a good listener.🙂

[@checkeredflagfilms]

Across the pond here. I raced vintage 2.0 liter back in the 80's equipped with 45's and a heavy modded engine. Today have a street version slightly modded 2.0 liter with injection. Once dialed in, never have to fiddle with it.

[@alfatechniks887]

Nice to hear. Do you retrofit MSD units in the states on your Nord engines? I’ve fitted a unit and I can’t fault it.

[@checkeredflagfilms]

@@alfatechniks887 I have a Crane Cams 'Fireball' XR3000 electronic points conversion for the ignition.

[@simonrowlands7472]

Great video, brings back memories of my alfa, I did it the same way to you and I thought it was spot on until I put it on the Rollers at GRV in littleborough and saw 90 bhp there guy had it on full chat then adjusted the dizzy it went straight up to 157 bhp ( swinging the dizzy) , I had gotten used to the power with driving it every day I stopped messing with it after that and just took it up to GRV

[@alfatechniks887]

Brillliant job then and great result 157bhp at wheels means it’s had work done. Much more than standard. Do you know what your ignition timing was and what it ended up at?

[@simonrowlands7472]

@@alfatechniks887 hi my engine had 45s and was gasflowed by grv the timing on the dizzy was set on the rolling Road and we never checked what degree it was, just max power

[@RichieRich845]

Thanks, I purchased the Gunson Color Tune and it worked great. My spark plugs were all black and the tail pipe was black too on my spider 2L.

[@alfatechniks887]

Glad it worked for you, running a bit rich. Could you smell it in the exhaust too?

[@RichieRich845]

@@alfatechniks887 yes, I'm going to clean the exhaust to see if the soot comes back as soon I bleed the brakes again. I recently replaced both boosters and the master cylinder and the rubber brake hoses from the brake fluid reservoir to the pipes going to the Mc (floor peddles). Having troublebleeding the air out, waiting for the Mityvac tool to arrive. The hoses were weeping brake fluid and destroyed the paint now the engine has to come out before I send it to get painted again. I would recommend if your hoses are old to replace them. I purchased 3 different "brake hoses" and the all wrapped after a week, finally found one that worked.

[@moggie100th]

Clever methods - thanks for sharing!

[@abuhamza1970]

Great vid, very informative and easy to understand even for a mechanical numpty like me - although in my defence my ‘89 Spider has fuel injection. Thanks for sharing

[@alfatechniks887]

Thank you for your feedback!

[@balicrimechannel8143]

I hope you don't mind my saying so, but I reckon you may be doing the spark plugs up a tad too tight. If you ever tighten spark plugs up using a torque wrench to the manufacturers specs, you'll be surprised how light a touch it is. It's actually just a fraction past finger-tight. If they repeatedly get overtightened, they start to leak combustion gasses and compression/ vacuum out/in through the compromised seal where the alloy collar meets the ceramic. This is identified by black/grey stainig in that area (not to be confused with brown 'corona' staining in the same spot which is normal and not caused by leaking gasses). I learned this when I had a vacuum leak I couldn't find, (causing rising and falling revs at idle) and it turned out to be the plugs I'd been over-tightening. It doesn't take much to damage the seal between the ceramic and the alloy because that alloy is soft and susceptible to the twisting motion of the socket. I saw that you noted that you'd already synced the butterflies before you started tuning with the idle screws, but I'll underline to people that you absolutely have to get the butterflies of the two carb bodies really synced first, otherwise you'll never be able to properly tune with the idle 'mixture' (really called 'volume') screws. I've seen lots of people use the idle volume (mixture) screws to try to tune out a problem that's actually being caused by un-synced butterflies. The most extreme casualty of this is when out of frustration, people screw the volume screws in too hard and damage the valve seat, thus ruining the carbs by making them untunable. P.S. I really like the exhaust temperature method you used. That's what propeller aircraft use by way of sensors and cockpit gauges.

[@alfatechniks887]

Hi thank you for your comprehensive comment. I do agree spark plugs don’t need to be overnight. I should state the recommended torque but didn’t in the video. And yes the top edge of the butterfly plates should just be visible on the first progression hole on across all cylinders to get baseline correct as a starter before synch balancing. Thanks again and really appreciated 👍

[@balicrimechannel8143]

@@alfatechniks887 I haven't used the progression hole method to sync the butterflies before but I'll have to give it a try. Actually I'd never thought to do that before. I usually use a feeler gauge made of a sliver of plastic drinking straw which works well. I open the butterflies, put the feeler at the bottom of the butterflies between the butterfly and the throttle bore then close the butterfly on top of it. Then I keep slowly turning the sync screw until I can just barely pull it out, then I repeat that on the other carb. Easier to do when the carbs are off though and approach it from the back end. I trust mechanical methods to tell me they're synced as opposed to vacuum readings because so many other things can affect vacuum, such as bleed screw position, leaks, varied cylinder compression, rising and falling revs while tuning etc.

[@raypurchase801]

Older engines should always be set to run slightly rich. It reduces the combustion heat and extends the life of your valves and head.

[@alfatechniks887]

Great feedback, thank you and very useful to know

[@JorgeComas1966]

Nice video, the method 3 ear sound it’s increíble...

[@alfatechniks887]

Have you tried it out on your car? Each cyclometer should sound the same with a distinctive ‘thump’ for each suck of the piston. A hissing sound means it could be running rich.

[@scuderiapraga6815]

@@alfatechniks887 love these videos thanks for sharing

[@etiennereijnders8848]

Thanks!, this helps alot!

[@alfatechniks887]

Great, any questions then please let me know

[@racingalfa80]

Nice one👍🏼

[@alfatechniks887]

Thanks for watching

[@priobe]

Great video But you did not show the temperature after the adjustment. I’m curious to see what temperature adjusted on 3&4 cylinders compared to 1&2

[@alfatechniks887]

Thanks for the message, jump to 6:25 and I recheck the temps which are within 5-10% of each other. Its not an exact number to look for but as long as they are within sensible value range and the engine runs smoothly then it would be acceptable

[@vinnychoff]

thanks i used your 3rd method to tune mine. i was just wondering about balancing?

[@alfatechniks887]

You can actually use the hose pipe method! You’re looking for ‘thump’ sound

[@alfatechniks887]

The thump sound should be equal across all cylinders. This is the sound of the air being drawn in. Otherwise you can use a synchrometer to measure air flows between the front and back twin carbs. If you have bypass screws then each cylinder can be optimised but start with them all turned in

[@rolanddemeyer8856]

Temp should be between 50 and 70 degrees for best respons Golden lodge as

[@alfatechniks887]

I will try these out and compare the results. Thanks for your advice it’s much appreciated

[@MilindaX]

Great use of the Gunson colourtune but when doing mine I found that if the flame colour is set to blue my car stumbles off idle. Revs don't pick up quickly and the throttle response is very slow. I've set my idle screwed to about 1.5 turns richer from the blue condition which seems to run much better. Any thoughts on as to why that may be?

[@alfatechniks887]

Sometimes these things are not an exact science and with carbs there are many more factors that can influence air fuel mixtures. It could be a number of things, check firstly though that the carbs are balanced and that ignition timing is set to the level of tune of your engine. I.e standard engine = standard ignition timing etc. When the car is idling it’s running in the idle circuit with butterfly’s closed and idle jets. As the butterfly’s open the main circuit comes in so it could be so to with this. Could be your jets are too big or incorrectly sized emulsion tubes.

[@donjackson3520]

Hi, great video. BTW, what should the fuel pressure be for best results? I’m not mechanic, I’m trying to tune my lotus 7.

[@alfatechniks887]

Hi Don, thank you for your message and feedback. Fuel pressure for a car running Weber or dellortors can be between 3-4psi. To confirm you have good stable pressure and to set your fuel pressure regulator it’s best to install an in-line low pressure gauge like mine so when you start the car from cold you can see pressure rise after it fills the float chambers in the carbs then start the car. People often just jump in and give a couple of pumps and then start which is only going to take longer. The carbs should also maintain pressure for a period of time after the engine is turned off. Hope the info helps

[@donjackson3520]

@@alfatechniks887 Hi, Thanks so much for the information, that’s very good of you. I have found a fuel regulator on line and an inline gauge (looks similar the one you have when I zoom in on the video). The lowest regulator I could find online here in North America is 4.5 to 9 PSI, so I will give it a try. The car had a very old electromechanical fuel pump that quit a couple of years ago. I could not find one the same, so I used a pump the delivers 7 PSI. I had no idea that the fuel pressure was so important. I’ll get this on order and installed when the car comes out of storage. Thanks again for your help.

[@alfatechniks887]

Hi sorry I’ve just seen your reply. Don’t go more than the minimum on that gauge your going to order 4.5 - 5 tops. Let me know if it works or send me a pic of your set up

[@donjackson3520]

@@alfatechniks887 hi, and thanks for the info. Do you mind if I ask, what make and or model is the fuel regulator you are using?

[@alfatechniks887]

@@donjackson3520hi it’s a malpassi competition filter king

[@rolanddemeyer8856]

First check ignition and adjust toen check synchronisation temp between 40 and 60 degrees ,

[@alfatechniks887]

Yes agree, the ignition has been set and carbs synchronised first, I just didn’t include that in this video

[@moggie100th]

Is there a model number of the Gunson Colortune that you used? Thanks

[@patrickcurda3295]

Good vid. What's the bore size for the Alfa 105 colourtune kit?

[@alfatechniks887]

I’m confident to that is a 16mm

[@jamesleggett2418]

Hi, I'm building an 1980 alfetta berlina, currently on the original dellortos. Have you ever used jenvey heritage throttle bodies?

[@alfatechniks887]

Hi no I haven’t and I see that they have the look of Weber’s , but have all the fun trickery of modern injection. Have you got them set up? Good luck with your build

[@jamesleggett2418]

@@alfatechniks887 i was considering sourcing a twin spark. i like the idea of matching numbers but without the faff of carbs. I'll let you know how it goes!

[@alfatechniks887]

Carbs are really very simple to set up and use on a daily basis. I didn’t know a thing about until I started playing with them and reading good books

[@betterpreparedness5167]

Thanks for producing that. What is the pressure gauge in the fuel line between the two carbs? I'm assuming you always have it in your carb set-up? Have not seen this before.

[@alfatechniks887]

Hi yes it’s a fuel pressure gauge so I can recalibrate my malpassi fuel regulator and it also allows me to confirm I have fuel pressure before turning the engine over. I originally fitted it as I was loosing fuel pressure due to leaking carb (stuck needle valve into the float chamber) but now I’ve fixed that the fuel remains at pressure way after I’ve turned the engine off.

[@finz1374]

I have single cam 70s bmw 4cyl engine with weber dcoe twins, I have weird issue that it backfires on only number 3 cylinder sometimes, any tips?

[@alfatechniks887]

Do you get popping back through the carb? If so it could be too lean and you need to adjust your idle mixture screw, turn it out or you have an air leak between your gasket or carb mount? Just guessing though

[@riccardorubino2571]

We have a Alfetta gtv 2.0. Our carbs were broken and bought a DHLA40E. We had a DHLA40G. Do you know the difference?

[@alfatechniks887]

Hi sorry for the delay. In short no and you may have to web search the differences. Assuming the G is a later carb and there will be minor differences. Things to look out for are air bypass screws, the 4 might have 4 progression holes and the G might have 5. Potentially one or both might be an emissions version? Minor changes changes in mouldings, e.g the idle mixture screws. I may have given you an idea but please search more on the web. Cheers

[@webersteve1547]

I have such carburators but I can't get the motor run on idle, the screw is allready screwed in completely. What can I do?

[@alfatechniks887]

Don’t screw the idles screws in completely. After you screw them gently, you need to back them off to by about 1.5 turns just to be in the ball park. Then adjust them for fine tuning

[@webersteve1547]

@@alfatechniks887 thank you. In the meantime I tried to understand the system better. As far as I understand it now, the idle is regulated by the four screw and not by the "endpoint" of the throttle lever? This said, with the four screws I'm not able to get the engine run idle

[@rickden8362]

Isn't there a proper air filter for those carbs?

[@alfatechniks887]

Hi yes it was taken off to use the pipe method, it can’t be done otherwise

[@rickden8362]

@@alfatechniks887 False economy. Maybe something like this would be an option: kzbin.info/www/bejne/i5KzqIioqbl9Y5Y

[@alfatechniks887]

I have individual air socks for each trumpet. Your solutions looks neat. Space is difficult on the Alfa’s especially the smaller engines

[@maxbg]

Cooler exhaust means running rich? So we have to turn in the idle mixture screw? For the Gunson plug, do you only hand tighted it?

[@alfatechniks887]

That’s correct, turn the idle screw in to lean more, the temp will rise and the result is almost instant. Blip the carbs and allow to settle to measure again and compare. The more comparisons you do the better. Turning the screw in too much will obviously prevent the fuel entering the combustion chamber at idle only so that cylinder will effective turn off and it will run like it’s running in 3. Hand tight is enough, possibly a light turn on the Allen key. Just needs nipping up after all it’s got to hold compression

[@idontcareaboutyou7757]

@@alfatechniks887 how can cooler exhaust mean it's running rich? if you lean it too much as you said it shuts off so temp will drop for not burning. i'm afraid you got a bit confused sir.

[@scottbrown4142]

Few years too late, but running lean gives hotter EGTs since all of the fuel going into the cylinder is burned, releasing all of its energy. Running rich means not all fuel is burned, the unburned fuel cools down the EGTs

[@johnjones4825]

Deep socket. Otherwise known as a plug spanner...

[@krusher74]

maybe a plug socket, but it's not a spanner

[@johnjones4825]

@@krusher74 lol!

[@rolanddemeyer8856]

Sorry i'm from belgium explain to me what a msd means

[@alfatechniks887]

MSD is a brand name 6Al is the model

[@rolanddemeyer8856]

Never use ngk or anny of these because it will burn holes thru the cylinders ALWAYS use golden lodges

[@alfatechniks887]

Interesting? It’s always had them since rebuild less than 15k km ago. Based on personal experiences.

[@superchargerone]

No it will not. Plenty of people run ngk. I have NGK in my 1750 for 20+ years and so have many others in AROC and never heard of anyone burning holes in their head. It is about selecting the correct plug temperature range for your state of tune. Golden lodges are not magic in and by themselves.

[@alfaromeo6878]

Never use golden lodge. The quality was ..., sorry, no, quality didn't exist! Only NGK!