Yes it's a DEFINITE risk ... Don't use the stock thin paper intake gaskets with those adaptors ... I've seen how they bend firsthand when I modified my relos 110 Loncin (March Hare Industries adaptor) ... I had to use it against my better judgement because he was whinging that he had paid for it and wanted it on the engine ...
We used one for THAT engine to raise the intake manifold so as to get enough clearance for the 22 mm Keihin carb and its deep float bowl ... I'd make one out of steel since you can get away with 6 to 10 mm thickness and it'll never bend ...
They bend where the two countersunk screws bolt the adaptor to the head ... The counter bores thin the metal section out and weaken the crap out of them ... You'd need to use silicone rubber type gaskets or sealant to allow for any gaps if they bent ... The March Hare adaptors have a rubber o-ring on the head side to get around the problem ... But that caused hassles for me as I had to open the centre of it out from 21 mm to 24 mm and went into the o-ring groove slightly due to the fact that the centre bore was out of whack with the centreline of the Loncin head port and intake manifold bore ... The adaptors were obviously made to suit CRF/XR 50 heads ...
You can most certainly lose power if you don't know what you are doing and hog a head out too big ... I only remove the absolute minimum amount of metal necessary to straighten out the flow ... if you lose too much velocity your bottom end grunt goes out the window ...
Whenever you increase port , carb or intake manifold bore sizes you are going to lose that strong kick off idle ... and there's nothing you can do about it ... I merely opened the stock Loncin 120's intake manifold out from 18 mm to match it to the stock head port and carb outlet and it lost it's off idle kick ... but it was a lot smoother and less abrupt which is better for the transmission ... They run everything small so that manual engines won't stall as easily for kids if they let the clutch out too quickly without increasing the revs or synchronising the clutch smoothly ...
Of course ported engines go heaps better when you twist the loud handle hard with the engine revving and use good clutch synchronisation and gear selection plus the right final drive ratio ... You can buy higher stall speed clutch weights and springs for CRF auto clutches to allow the engine to rev higher on take off ...
Here's a pic of Loncin intake manifolds .... (Left) Stocker ~ 18 mm bore ... (centre) Port matched to stock carb and head port ~ 21 mm bore and (right) matched to ported head and 22 mm Keihin ... 24 mm bore ... Loncins are pretty close to an exact CRF engine copy and have the exact same cylinder stud spacings ...
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