zev Posted February 20 Share Posted February 20 Hey Friends, I’m hoping people can offer some insights on a tuning issue I’m having with my 45 DCOE’s The car is a 72 240 with a rebello 3L stroker. Dave strongly suggested using the Chinese knockoff FAJS carbs, saying the machine work on these was much better than what he had seen coming directly from Weber, so that’s what we went with. He tuned the motor on his dyno and it runs beautifully all through the rev range with one big exception. Right at “tip-in” when I’m transitioning from fully closed throttle to say 1/8 or even 1/16 throttle there is ZERO progression, meaning that the throttle is either on or off, and this happens regardless of speed and RPM. Off the line I have to feather the clutch to keep the transition smooth which is fine, but if I’m heading into a corner and transitioning from the brakes to the throttle, there’s no way to get back on throttle without a big jerk, which in turn greatly upsets the suspension of the car. It feels like I have to overcome so much vacuum at the petal that there’s just no in-between from on or off throttle. So far I’ve tried bigger pump jets and tried blocking the economizers at the bottom of the float bowl and that made zero difference. I don’t think the issue is in the pilot jets since it doesn’t even feel like I’m getting into the pilot jet yet…it’s literally just the transition from fully closed throttle to ANY amount of throttle no matter how small. These carbs have 5 progression holes and Dave recommended drilling one of them out slightly, but before I go that route I wanted to see what other people think. I’m all for switching to genuine Webers if that would help, but both Dave Rebello and Dave at Pierce manifolds said the FAJS carbs are every bit as good. This stumble greatly affects the drive ability of the car so I’ll try anything to get it solved. many thanks. Quote Link to comment Share on other sites More sharing options...
jonbill Posted February 21 Share Posted February 21 I'd look at where the throttle plate is, in relation to the progression holes. You want it to start uncovering a progression hole at the first movement of the throttle. I think it is possible to setup idle by keeping the idle bypass screws shut and opening the throttle to the first progression hole, but you've then got a fair way to go to the next progression hole. Correct way is to have idle on completely closed throttle and idle air supplied by the bypass screws. Quote Link to comment Share on other sites More sharing options...
munters Posted February 22 Share Posted February 22 Or go a complete new way of tuning with Keith Frank at https://vintagetechnologygarage.groups.io/g/sidedraft/topic/100219752#4322 He has a big knowledge of the DCOE carbs and helps to the end of tuning. I went his route and find them way better and easier to tune compared to the original weber. He has his new kind of jets at this store. https://www.webstore.com/user,pgr,82598,ac,82598,owner_id,other_items 1 Quote Link to comment Share on other sites More sharing options...
tube80z Posted February 23 Share Posted February 23 On 2/22/2024 at 12:48 AM, munters said: Or go a complete new way of tuning with Keith Frank at https://vintagetechnologygarage.groups.io/g/sidedraft/topic/100219752#4322 He has a big knowledge of the DCOE carbs and helps to the end of tuning. I went his route and find them way better and easier to tune compared to the original weber. Can you give a summary of what this method is? I went to that link, which required a signup and only found a group with a ton of emails. Quote Link to comment Share on other sites More sharing options...
Datsunpowers Posted February 24 Share Posted February 24 Zev, a couple ideas come to mind. You said you tried larger pump jets, but it sounds like you are not getting enough accelerator pump fuel delivered to the intake stream when it transitions off of the idle circuit. With 45MM carbs with large ventures. When you open the throttle the air velocity slows way down, and the fuel will drop out of the air steam. You need a good shot of fuel to overcome this. Double check that the accelerator jets are squirting forward and at the same velocity. I had the same stumbling issue and two of the accelerator jets were clogged with debris on my carbs. The only way I found this was taking the carb of and watching the fuel come out of the accelerator pump jets. It drove me crazy until I found this issue. If you have a wideband controller installer you could see this lean condition when you open the throttle and transition off the idle circuit to the main fuel circuit. If you PM me. I can share my jetting chart that has worked for my 45mm Solexes. At least you have some more data as jets are expense. Hope this helps. Quote Link to comment Share on other sites More sharing options...
munters Posted February 28 Share Posted February 28 Those are the new emulsion tubes he created. He also made new idle jets for weak vacuum(normal with a hotter cam) my 2.75L engine produces 275bhp with 45dcoes and 37mm venturies and runs close to a injected engine except the difference in hot/cold and high/low altitude. You can subscribe, give him your engine and dcoe specs, tell him your problem and he will help with a lot of patience and knowledge until it works. 1 Quote Link to comment Share on other sites More sharing options...
Leon Posted March 15 Share Posted March 15 On 2/20/2024 at 2:55 PM, zev said: Hey Friends, I’m hoping people can offer some insights on a tuning issue I’m having with my 45 DCOE’s The car is a 72 240 with a rebello 3L stroker. Dave strongly suggested using the Chinese knockoff FAJS carbs, saying the machine work on these was much better than what he had seen coming directly from Weber, so that’s what we went with. He tuned the motor on his dyno and it runs beautifully all through the rev range with one big exception. Right at “tip-in” when I’m transitioning from fully closed throttle to say 1/8 or even 1/16 throttle there is ZERO progression, meaning that the throttle is either on or off, and this happens regardless of speed and RPM. Off the line I have to feather the clutch to keep the transition smooth which is fine, but if I’m heading into a corner and transitioning from the brakes to the throttle, there’s no way to get back on throttle without a big jerk, which in turn greatly upsets the suspension of the car. It feels like I have to overcome so much vacuum at the petal that there’s just no in-between from on or off throttle. So far I’ve tried bigger pump jets and tried blocking the economizers at the bottom of the float bowl and that made zero difference. I don’t think the issue is in the pilot jets since it doesn’t even feel like I’m getting into the pilot jet yet…it’s literally just the transition from fully closed throttle to ANY amount of throttle no matter how small. These carbs have 5 progression holes and Dave recommended drilling one of them out slightly, but before I go that route I wanted to see what other people think. I’m all for switching to genuine Webers if that would help, but both Dave Rebello and Dave at Pierce manifolds said the FAJS carbs are every bit as good. This stumble greatly affects the drive ability of the car so I’ll try anything to get it solved. many thanks. If this happens regardless of speed or RPM, as you say, then I'm highly suspicious of your throttle linkage. Can you post a pic of your setup? If it's mechanical linkage, check for binding. If it's a throttle cable, I wonder if your lever ratio (length of carb throttle rod / cable throttle rod) is too aggressive. In other words, you may need a longer cable throttle rod. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.