CB72 head??

hondaly · Post by **hondaly** » Fri Aug 24, 2018 8:50 am

Hello Everyone, I have just built up my CB72 engine after a rebore, pistons etc. I used a different 72? head I had been given, fitted new cam bearings, ground in valves etc. I had measured the inlet port at 23.6mm and felt this was right for 22mm carbs.
On finishing the rebuild I realised the head had not been drilled and tapped for the "power jet" nipples for tube to air filters. Is this ok?? Was there a mod? Thoughts please.

LOUD MOUSE · Post by **LOUD MOUSE** » Fri Aug 24, 2018 9:04 am

The power jets which went to the filters came one from each carb.
Do you recall if the steel dome has a relief cast at the edg of the dome that went down a couple of mill or did the dome come sharp to the edge?. ..............lm

hondaly wrote:Hello Everyone, I have just built up my CB72 engine after a rebore, pistons etc. I used a different 72? head I had been given, fitted new cam bearings, ground in valves etc. I had measured the inlet port at 23.6mm and felt this was right for 22mm carbs.
On finishing the rebuild I realised the head had not been drilled and tapped for the "power jet" nipples for tube to air filters. Is this ok?? Was there a mod? Thoughts please.

hondaly · Post by **hondaly** » Sat Aug 25, 2018 5:37 am

Thanks for your reply Loud Mouse, I always read your posts with interest. Unfortunately I did not check the dome dia or whether it was chamfered at the edge. I thought because the inlet was 23.6mm it was for 22mm carbs and therefore a cb72 head. Is the inlet dia in the casting different for a 77 head? My old head had the drilled and tapped holes for the air vent joint/nipple, the passage seems to connect to the inlet valve guide. If it is a "72" head, can I use it without the air vent holes? I am trying to determine this without taking the head off ! I would be grateful for your thoughts. Al.

LOUD MOUSE · Post by **LOUD MOUSE** » Sat Aug 25, 2018 6:33 am

The head without the 2 threaded valve vent holes came along sometime in late 66/67.
I'm not sure if the 250 had this or not so as much as I hate to tell you.
If that was my engine I'd remove and check the design of the dome.
Big difference in compression. ......................lm

hondaly wrote:Thanks for your reply Loud Mouse, I always read your posts with interest. Unfortunately I did not check the dome dia or whether it was chamfered at the edge. I thought because the inlet was 23.6mm it was for 22mm carbs and therefore a cb72 head. Is the inlet dia in the casting different for a 77 head? My old head had the drilled and tapped holes for the air vent joint/nipple, the passage seems to connect to the inlet valve guide. If it is a "72" head, can I use it without the air vent holes? I am trying to determine this without taking the head off ! I would be grateful for your thoughts. Al.

hondaly · Post by **hondaly** » Sat Aug 25, 2018 8:12 am

Thanks LM Yes I have decided to take head off and check dome. better done now than later. Al

LOUD MOUSE · Post by **LOUD MOUSE** » Sat Aug 25, 2018 8:38 am

Good on ya Al. ................lm

hondaly wrote:Thanks LM Yes I have decided to take head off and check dome. better done now than later. Al

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