I have a '68 144 with the B18B. Never seemed to run very well since I got it few years back. Past owner had the same lack of power issue. I have added a '75 dizzy. Two years ago I pulled the BW35 and put in a M41. Just not able to get in any driving time. I just posted about a broken HIF6 idel screw that I corrected with a replacement body.

Appears to be getting fuel to carb. Just seems like engine does want to draw it in. Has replacment fuel pump and filter. Disconnected line at carb and put in container and cranked to check fuel flow. Put gauge on while running. Show about 3lbs. Carbs are rebuilt with new needle and seat, throttle seals and rebuilt cold start. Float adjusted. Carbs preset. I switched from HS6 to HIF6 as my shafts were worn on the HS6.

It will start after lots cranking cold. Choke out and cold start active. If I dripple some gas in it fires right up. Once running it will idle pretty well but isn't well enough to drive it. Dies and stumbles bad. I pulled manifold and replaced with all in one cast without secondaries. Used new gasket and made sure intake rings in place. I seem have better results with hose going to power brakes and flame trap plugged. Brake boaster seems ok. Will double check. Seems like I have a major vacumm issue somewhere. Compression tested at 170 pretty even on cold engine. Valves are adjusted. Could I have a stuck valve and if so how would one know? Put a vacuum gauge on the engine?